Numerical Simulation Study on the Effect of Horizontal Well Reservoir Stimulation for Gas Hydrate Production

A new gas hydrate reservoir stimulation method of in-situ fracturing with transient heating is proposed, in line with analysis of the technological bottlenecks faced by marine gas hydrate production. This method injects the developed chemical reagents into a hydrate reservoir through hydraulic fracturing, releasing heat during the chemical reaction to increase the hydrate decomposition rate. The chemical reaction product furthermore has a honeycomb structure to support fractures and increase reservoir permeability. Based on the geological model of natural gas hydrate in the South China Sea, three development methods are simulated to evaluate hydrate production capacity, consisting of horizontal well, fractured horizontal well and in-situ fracturing with transient heating well. Compared with the horizontal well, the simulation results show that the cumulative gas production of the fractured horizontal well in one year is 7 times that of the horizontal well, while the cumulative gas production of in-situ fracturing with transient heating well is 12 times that of the horizontal well, which significantly improves daily efficiency and cumulative gas production. In addition, the variation patterns of hydrate saturation and temperature-pressure fields with production time for the three exploitation plans are presented, it being found that three sensitive parameters of fracture conductivity, fracture half-length and fracture number are positively correlated with hydrate production enhancement. Through the simulations, basic data and theoretical support for the optimization of gas hydrate reservoir stimulation scheme has been provided.

Progress and development directions of stimulation techniques for ultra-deep oil and gas reservoirs

By reviewing the development history of stimulation techniques for deep/ultra-deep oil and gas reservoirs,the new progress in this field in China and abroad has been summed up,including deeper understanding on formation mechanisms of fracture network in deep/ultra-deep oil and gas reservoir,performance improvement of fracturing fluid materials,fine stratification of ultra-deep vertical wells,and mature staged multi-cluster fracturing technique for ultra-deep and highly deviated wells/horizontal wells.In light of the exploration and development trend of ultra-deep oil and gas reservoirs in China,the requirements and technical difficulties in ultra-deep oil and gas reservoir stimulation are discussed:(1)The research and application of integrated geological engineering technology is difficult.(2)The requirements on fracturing materials for stimulation are high.(3)It is difficult to further improve the production in vertical profile of the ultra-deep and hugely thick reservoirs.(4)The requirements on tools and supporting high-pressure equipment on the ground for stimulation are high.(5)It is difficult to achieve efficient stimulation of ultra-deep,high-temperature and high-pressure wells.(6)It is difficult to monitor directly the reservoir stimulation and evaluate the stimulation effect accurately after stimulation.In line with the complex geological characteristics of ultra-deep oil and gas reservoirs in China,seven technical development directions are proposed:(1)To establish systematic new techniques for basic research and evaluation experiments;(2)to strengthen geological research and improve the operational mechanism of integrating geological research and engineering operation;(3)to develop high-efficiency fracturing materials for ultra-deep reservoirs;(4)to research separated layer fracturing technology for ultra-deep and hugely thick reservoirs;(5)to explore fracture-control stimulation technology for ultra-deep horizontal well;(6)to develop direct monitoring technology for hydraulic fractures in ultra-deep oil and gas reservoirs;(7)to develop downhole fracturing tools with high temperature and high pressure tolerance and supporting wellhead equipment able to withstand high pressure.

Simulation of Two-Phase Flowback Phenomena in Shale Gas Wells

The gas-water two-phaseflow occurring as a result of fracturingfluidflowback phenomena is known to impact significantly the productivity of shale gas well.In this work,this two-phaseflow has been simulated in the framework of a hybrid approach partially relying on the embedded discrete fracture model(EDFM).This model assumes the region outside the stimulated reservoir volume(SRV)as a single-medium while the SRV region itself is described using a double-medium strategy which can account for thefluid exchange between the matrix and the micro-fractures.The shale gas adsorption,desorption,diffusion,gas slippage effect,fracture stress sensitivity,and capillary imbibition have been considered.The shale gas production,pore pressure distribution and water saturation distribution in the reservoir have been simulated.The influences of hydraulic fracture geometry and nonorthogonal hydraulic fractures on gas production have been determined and discussed accordingly.The simulation results show that the daily gas production has an upward and downward trend due to the presence of a large amount of fracturingfluid in the reservoir around the hydraulic fracture.The smaller the angle between the hydraulic fracture and the wellbore,the faster the daily production of shale gas wells decreases,and the lower the cumulative production.Nonplanar fractures can increase the control volume of hydraulic fractures and improve the production of shale gas wells.

The “fracture-controlled reserves” based stimulation technology for unconventional oil and gas reservoirs

To solve the problems facing the economic development of unconventional oil and gas, a new concept and corresponding technology system of reservoir stimulation based on "fracture-controlled reserves" are put forward. The "fracture-controlled reserves" stimulation technology is to realize the three-dimensional producing and economic and efficient development of unconventional hydrocarbon resources by forming a fracture system that well matches "sweet spots" and "non-sweet spots". The technical route of the stimulation technology is "three optimizations and controls", that is, control the scope of sand body through optimizing well spacing, control the recoverable reserves through optimizing fracture system, and control the single well production reduction through optimizing energy complement method. The "fracture-controlled reserves" stimulation emphasizes the maximization of the initial stimulation coefficient, the integration of energy replenishment, stimulation and production, and prolonging the re-fracturing cycle or avoiding re-fracturing. It aims at realizing the three-dimensional full producing and efficient development of reservoir in vertical and horizontal directions and achieving the large-scale, sustainable and high profitable development of unconventional oil and gas resources. The stimulation technology was used to perform 20 pilot projects in five typical tight-oil, shale gas blocks in China. The fracturing and producing effects of tight oil improved and the commercial development for shale gas was realized.

Shale oil and gas exploitation in China:Technical comparison with US and development suggestions

The shale oil and gas exploitation in China is technically benchmarked with the United States in terms of development philosophy,reservoir stimulation treatment,fracturing parameters,fracturing equipment and materials,oil/gas production technology,and data/achievements sharing.It is recognized that the shale oil and gas exploitation in China is weak in seven aspects:understanding of flow regimes,producing of oil/gas reserves,monitoring of complex fractures,repeated stimulation technology,oil/gas production technology,casing deformation prevention technology,and wellbore maintenance technology.Combined with the geological and engineering factors of shale oil and gas in China,the development suggestions of four projects are proposed from the macro-and micro-perspective,namely,basic innovation project,exploitation technology project,oil/gas production stabilization project,and supporting efficiency-improvement project,so as to promote the rapid,efficient,stable,green and extensive development of shale oil and gas industry chain and innovation chain and ultimately achieve the goal of“oil volume stabilizing and gas volume increasing”.

Proppant transport in rough fractures of unconventional oil and gas reservoirs

A method to generate fractures with rough surfaces was proposed according to the fractal interpolation theory.Considering the particle-particle,particle-wall and particle-fluid interactions,a proppant-fracturing fluid two-phase flow model based on computational fluid dynamics(CFD)-discrete element method(DEM)coupling was established.The simulation results were verified with relevant experimental data.It was proved that the model can match transport and accumulation of proppants in rough fractures well.Several cases of numerical simulations were carried out.Compared with proppant transport in smooth flat fractures,bulge on the rough fracture wall affects transport and settlement of proppants significantly in proppant transportation in rough fractures.The higher the roughness of fracture,the faster the settlement of proppant particles near the fracture inlet,the shorter the horizontal transport distance,and the more likely to accumulate near the fracture inlet to form a sand plugging in a short time.Fracture wall roughness could control the migration path of fracturing fluid to a certain degree and change the path of proppant filling in the fracture.On the one hand,the rough wall bulge raises the proppant transport path and the proppants flow out of the fracture,reducing the proppant sweep area.On the other hand,the sand-carrying fluid is prone to change flow direction near the contact point of bulge,thus expanding the proppant sweep area.

A Feasibility Study of Using Geothermal Energy to Enhance Natural Gas Production from Offshore Gas Hydrate Reservoirs by CO_(2) Swapping

The energy industry faces a significant challenge in extracting natural gas from offshore natural gas hydrate(NGH)reservoirs,primarily due to the low productivity of wells and the high operational costs involved.The present study offers an assessment of the feasibility of utilizing geothermal energy to augment the production of natural gas from offshore gas hydrate reservoirs through the implementation of the methane-CO_(2)swapping technique.The present study expands the research scope of the authors beyond their previous publication,which exclusively examined the generation of methane from marine gas hydrates.Specifically,the current investigation explores the feasibility of utilizing the void spaces created by the extracted methane in the hydrate reservoir for carbon dioxide storage.Analytical models were employed to forecast the heat transfer from a geothermal zone to an NGH reservoir.A study was conducted utilizing data obtained from a reservoir situated in the Shenhu region of the Northern South China Sea.The findings of the model indicate that the implementation of geothermal heating can lead to a substantial enhancement in the productivity of wells located in heated reservoirs during CO_(2)swapping procedures.The non-linear relationship between the temperature of the heated reservoir and the rate of fold increase has been observed.It is anticipated that the fold of increase will surpass 5 when the gas hydrate reservoir undergoes a temperature rise from 6℃ to 16℃.The mathematical models utilized in this study did not incorporate the impact of heat convection resulting from CO_(2)flow into the gas reservoir.This factor has the potential to enhance well productivity.The mathematical models’deviation assumptions may cause over-prediction of well productivity in geothermal-stimulated reservoirs.Additional research is required to examine the impacts of temperature drawdown,heat convection resulting from depressurization,heat-induced gas pressure increment,and the presence of free gas in the formation containing hydrates.The process of CH4-CO_(2)swapping,which has been investigated,involves the utilization of geothermal stimulation.This method is highly encouraging as it enables the efficient injection of CO_(2)into gas hydrate reservoirs,resulting in the permanent sequestration of CO_(2)in a solid state.Additional research is warranted to examine the rate of mass transfer of CO_(2)within reservoirs of gas hydrates.

The status of exploitation techniques of natural gas hydrate

Natural gas hydrate(NGH)has been widely considered as an alternative form of energy with huge potential,due to its tremendous reserves,cleanness and high energy density.Several countries involving Japan,Canada,India and China have launched national projects on the exploration and exploitation of gas hydrate resources.At the beginning of this century,an early trial production of hydrate resources was carried out in Mallik permafrost region,Canada.Japan has conducted the first field test from marine hydrates in 2013,followed by another trial in 2017.China also made its first trial production from marine hydrate sediments in 2017.Yet the low production efficiency,ice/hydrate regeneration,and sand problems are still commonly encountered;the worldwide progress is far before commercialization.Up to now,many gas production techniques have been proposed,and a few of them have been adopted in the field production tests.Nevertheless,hardly any method appears really promising;each of them shows limitations at certain conditions.Therefore,further efforts should be made on the economic efficiency as well as sustainability and environmental impacts.In this paper,the investigations on NGH exploitation techniques are comprehensively reviewed,involving depressurization,thermal stimulation,chemical inhibitor injection,CO2–CH4 exchange,their combinations,and some novel techniques.The behavior of each method and its further potential in the field test are discussed.The advantages and limitations of laboratory studies are also analyzed.The work could give some guidance in the future formulation of exploitation scheme and evaluation of gas production behavior from hydrate reservoirs.

The second natural gas hydrate production test in the South China Sea

Clayey silt reservoirs bearing natural gas hydrates(NGH)are considered to be the hydrate-bearing reservoirs that boast the highest reserves but tend to be the most difficult to exploit.They are proved to be exploitable by the first NGH production test conducted in the South China Sea in 2017.Based on the understanding of the first production test,the China Geological Survey determined the optimal target NGH reservoirs for production test and conducted a detailed assessment,numerical and experimental simulation,and onshore testing of the reservoirs.After that,it conducted the second offshore NGH production test in 1225 m deep Shenhu Area,South China Sea(also referred to as the second production test)from October 2019 to April 2020.During the second production test,a series of technical challenges of drilling horizontal wells in shallow soft strata in deep sea were met,including wellhead stability,directional drilling of a horizontal well,reservoir stimulation and sand control,and accurate depressurization.As a result,30 days of continuous gas production was achieved,with a cumulative gas production of 86.14×104 m3.Thus,the average daily gas production is 2.87×10^4 m^3,which is 5.57 times as much as that obtained in the first production test.Therefore,both the cumulative gas production and the daily gas production were highly improved compared to the first production test.As indicated by the monitoring results of the second production test,there was no anomaly in methane content in the seafloor,seawater,and atmosphere throughout the whole production test.This successful production test further indicates that safe and effective NGH exploitation is feasible in clayey silt NGH reservoirs.The industrialization of hydrates consists of five stages in general,namely theoretical research and simulation experiments,exploratory production test,experimental production test,productive production test,and commercial production.The second production test serves as an important step from the exploratory production test to experimental production test.

Progress and prospects of oil and gas production engineering technology in China

This paper summarizes the important progress in the field of oil and gas production engineering during the"Thirteenth Five-Year Plan"period of China,analyzes the challenges faced by the current oil and gas production engineering in terms of technological adaptability,digital construction,energy-saving and emission reduction,and points out the future development direction.During the"Thirteenth Five-Year Plan"period,series of important progresses have been made in five major technologies,including separated-layer injection,artificial lift,reservoir stimulation,gas well de-watering,and workover,which provide key technical support for continuous potential tapping of mature oilfields and profitable production of new oilfields.Under the current complex international political and economic situation,oil and gas production engineering is facing severe challenges in three aspects:technical difficulty increases in oil and gas production,insignificant improvements in digital transformation,and lack of core technical support for energy-saving and emission reduction.This paper establishes three major strategic directions and implementation paths,including oil stabilization and gas enhancement,digital transformation,and green and low-carbon development.Five key research areas are listed including fine separated-layer injection technology,high efficiency artificial lift technology,fine reservoir stimulation technology,long term gas well de-watering technology and intelligent workover technology,so as to provide engineering technical support for the transformation,upgrading and high-quality development of China’s oil and gas industry.

Effect of Thermal Defocusing on Backward Stimulated Raman Scattering in CH4

The conversion efficiency of stimulated Raman scattering （SRS） in CH4 is studied by using a single longitudinal mode second-harmonic Nd：YAG laser （532 nm, linewidth 0.003 cm^-1, pulse-width （FWHM） 6.5 ns）. Due to the heat release from vibrationally excited particles, SRS processes often suffer from the thermal defocusing effect （TDE）. In view of 6.5 ns laser pulse width is much shorter than the vibrational relaxation time of CH4 molecules, TDE can only affect the SRS processes afterwards. In the cases of low laser repetition, TDE will be not serious, because it will be removed by the thermal diffusion in Raman medium before the next pulse arrives. At the laser repetition rate 2 Hz, CH4 pressure 1.1 MPa and pump laser energy 95 mJ, the quantum conversion efficiency of backward first-Stokes （BS1） has attained 73%. This represents the highest first-stokes conversion efficiency in CH4. Furthermore, due to the relaxation oscillation, the BS1 pulses are narrowed to about 1.2 ns. As a result, the BS1 peak power turns out to be 2.7 times that of the pump. Its beam quality is also much better and is only slightly affected by TDE. This reason is that BS1 represents a wave-front-reversed replica of the pump beam, which can compensate the thermal distortions in Raman amplify process. Under the same conditions, but pump laser repetition rate as 10 Hz, the conversion efficiency of BS1 goes down to 36% due to TDE. From this study, we expect that a well-behaved 630 nm Raman laser may be designed by using a closed CH4/He circulating-cooling system, which may have some important applications.

Dominating factors on well productivity and development strategies optimization in Weiyuan shale gas play, Sichuan Basin, SW China

Weiyuan shale gas play is characterized by thin high-quality reservoir thickness,big horizontal stress difference,and big productivity differences between wells.Based on integrated evaluation of shale gas reservoir geology and well logging interpretation of more than 20 appraisal wells,a correlation was built between the single well test production rate and the high-quality reservoir length drilled in the horizontal wells,high-quality reservoir thickness and the stimulation treatment parameters in over 100 horizontal wells,the dominating factors on horizontal well productivity were found out,and optimized development strategies were proposed.The results show that the deployed reserves of high-quality reservoir are the dominating factors on horizontal well productivity.In other words,the shale gas well productivity is controlled by the thickness of the high-quality reservoir,the high-quality reservoir drilling length and the effectiveness of stimulation.Based on the above understanding,the development strategies in Weiyuan shale gas play are optimized as follows:(1)The target of horizontal wells is located in the middle and lower parts of Longyi 11(Wei202 area)and Longyi 11(Wei204 area).(2)Producing wells are drilled in priority in the surrounding areas of Weiyuan county with thick high-quality reservoir.(3)A medium to high intensity stimulation is adopted.After the implementation of these strategies,both the production rate and the estimated ultimate recovery(EUR)of individual shale gas wells have increased substantially.

Practice and understanding of sidetracking horizontal drilling in old wells in Sulige Gas Field, NW China

To seek effective ways of lowering development cost and tapping inter-well remaining reserves, sidetracking horizontal wells from old wells in Su10 and Su53 Block were conducted. The engineering and geological problems such as leakage, collapse and sticking in slim-hole sidetracking, and difficult evaluation of remaining gas were gradually overcome, and a set of drilling and completion technology, well deployment optimization technology and geo-steering technology suitable for sidetracking horizontal wells in tight sandstone gas reservoirs have been worked out. By making full use of the old well, sidetracking horizontal wells can greatly reduce development costs, enhance the producing degree of inter-well remaining reserves, and get production 3-5 times of that of adjacent vertical wells.Its production effect is influenced by encountered sandstone length, the position of the horizontal segment in the reservoir, produced effective reservoir thickness, gas saturation, controlled reserves and fracturing effect, etc. Up to now, in Block Su10 and Su53, 12 sidetracking horizontal wells have been drilled, which have an average drilling cycle of 49 days, average horizontal section length of 689 m,average effective drilling ratio of 61.5%, average well-head pressure of 16.2 MPa, and daily output of 4.7×10~4 m^3 at the initial stage after production. By the end of 2017, the average yield increment was more than 1 000×10~4 m^3 with good effect. With the increase of low yield old wells, wells in the enrichment regions tend to be saturated and the rest gas-bearing areas are lower in grade, therefore, sidetracking horizontal well can be used for optimization of well pattern, well deployment mode and exploitation of remaining oil areas.

Development of Moxi Gas Field, Sichuan Basin

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Effect of thermal stimulation on gas production from hydrate deposits in Shenhu area of the South China Sea

The Shenhu area on the northern continental slope of the South China Sea （SCS） is one of the promising fields for gas hydrate exploitation. The hydrate-bearing layer at drilling site SH2 is overlain and underlain by permeable zones of mobile water. In this study a vertical well was configured with a perforated Interval I for producing gas and a coiled Interval II for heating sed- iment, The hydrate is dissociated by a small depressurization at Interval Ⅰ and a thermal stimulation at Interval Ⅱ. The numeri- cal simulations indicate that the thermal stimulation has a significant effect on gas release from the hydrates in the production duration and improves the gas production in the late period. The gas released by thermal stimulation cannot be produced as quickly as the production gets operated because of the hard pathway for fluids to flow in the sediments. The gas production is enhanced due to the heating for 7242 m3 in the whole production. Increasing heating temperature at Interval Ⅱcan improve gas production and restrain water output, and advance the arrival time of the gas flow from the zone at Interval Ⅱ. The absolute criterion and relative criterion suggest that the thermal stimulation in the production schemes is pronounced for releasing gas from the hydrate deposit, but the production efficiency of gas is limited by the sediment of low permeability. The study pro- vides an insight into the production potential of the hydrate accumulations by thermal stimulation with depressurization in two wells, and a basis for analyzing economic feasibility of gas production from the area.

Effect of electric acupoint stimulation on gastrointestinal hormones and motility among geriatric postoperative patients with gastrointestinal tumors

OBJECTIVE:To evaluate the effects of electric acupoint stimulation on gastrointestinal hormones and motility among geriatric postoperative patients with gastrointestinal tumors,and to explore an efficient and noninvasive method for postoperative recovery of bowel functions.METHODS:Forty patients were randomly and evenly assigned into a regular nursing care group(RNC) and an acupoint electric stimulation group(AES).Patients in the RNC group received regular nursing care and patients in the AES group received regular nursing care plus electric stimulation of acupoints.The serum levels of gastrin(GAS),motilin(MOT),and cholecystokinin(CCK),and an electrogastrogram(EGG) of all the patients were evaluated on the first,third,and fifth day after surgery.The time to first flatus after surgery and the number of patients with side effects such as abdominal pain,abdominal distention,and diarrhea were recorded.RESULTS:There were significant differences between the two groups in GAS,MOT,EGG,time to first flatus,abdominal pain,abdominal distention,and diarrhea(P < 0.05).CONCLUSION:Electric stimulation on acupoints could increase levels of GAS and MOT,promote the recovery of gastrointestinal functions,and decrease complications among postoperative senile patients with gastrointestinal tumors.

Large borehole with multi-lateral branches: A novel solution for exploitation of clayey silt hydrate

Raising the in situ decomposition rate of natural gas hydrate and increasing the decomposition contact area are two main ways to raise the productivity of hydrate. An exploitation technique based on large borehole with multi-lateral branches (LB & MB) was proposed in this paper. This technique is mainly intended for the clayey silt hydrate reservoir in the South China Sea, and its main purpose is to alleviate the sand output from formation for maintaining the stability of the reservoir and to greatly increase the gas productivity of the reservoir. In this paper, the following aspects were mainly expounded: definition of the basic geometric parameters for layout of multi-lateral branches in clayey silt hydrate reservoir, simulation of the stimulation effect of a typical well profile with two branches, and prediction and simulation of the reservoir failure risk in a well profile with eight branches. The results show that the LB & MB effectively improves the flow field in the formation, raises the productivity of the reservoir and may also help to decrease the produced water-gas ratio (WGR). When the lateral branches spacing is too small, the failure zones around adjacent lateral branches overlap each other, possibly causing reservoir failure in a larger range. Therefore, the geometric parameters of multi-lateral branches depend on the dual control of the productivity and geotechnical risk factor of reservoir. Further study is being carried out, so as to obtain the optimal combination of parameters of multi-lateral branches.

Mechanics and fracturing techniques of deep shale from the Sichuan Basin, SW China

Deep shale gas exploration and production in Fuling(Sichuan Basin,SW China)are confronted with hydraulic fracturing challenges owing to high stress,high fracture pressure,low pump rate and proppant concentration,as well as high closing pressure in deep strata.This study focused on the mechanical properties of shale core samples from Fuling through high-temperature triaxial rock mechanical tests and in-situ stress tests based on the Kessel effect of acoustic emission.Their mechanical property var-iations with depth were delineated using brittleness index calculated via simulating different depths and different confining pressures for the samples.The results showed that several parameters of deep shale reservoirs,i.e.brittleness index,fracture density,performance of self-propping,and flow conductivity,are lower than that of shale reservoirs with moderate burial depth.Thus,the current operating pressure in deep shale reservoir stimulation should be taken full advantage of,rather than channeling the focus on the propagation of fracture length.The objective is to increase the complexity of the near-hole fracture network for enhancing self-propping and flow conductivity of the fractures.This can be achieved by reducing the number of perforation clusters and cluster spacing,adopting variable-rate fracturing,decreasing proppant size,increasing sand volume,and optimizing the fracturing parameters.A field application showed that,compared with the neighboring wells,the test well had larger drainage area,doubling the gas yield.

MATHEMATICAL AND COMPUTER SIMULATION TECHNOLOGY OF CONDENSATE OIL AND GAS WELLS STIMULATED BY ELECTROMAGNETIC HEATING

In this article, the recent research achievements on the theory and technology of condensate oil and gas wells stimulated by electromagnetic induction heating during middle or late exploitation period were introduced for the first time at home and abroad. A new kind of electromagnetic wave induction heating equipment XAEMH-1 was developed. Taking near wellbore zone temperature field as the main research object, which is the key factor for the condensation and retrograde vaporization during electromagnetic heating, the mathematical simulation model for a condensate oil and gas well stimulated by electromagnetic heating to eliminate blockage near wellbore region was established. A corresponding computer system was developed to dynamically predict and evaluate the efficiency of this electromagnetic heating process. Through this computer system, the near wellbore region distributions of several important factors such as temperature, pressure, condensate oil saturation and relative permeability can be described quantitatively. A condensate gas well in a late exploitation period reservoir here in China was chosen as a practical example to test the effectiveness of this new technology and some satisfactory results were obtained. These results proved that it is feasible to eliminate the near wellbore region blockage by electromagnetic heating. A new prospective stimulation method was given for the condensate oil and gas reservoirs during middle or late exploitation period.

Theories and practices of carbonate reservoirs development in China

Carbonate reservoirs in China have the characteristics of diversified accumulation pattern, complex structure and varying reservoir conditions. Concerning these characteristics, this article tracks the technical breakthroughs and related practices since the 1950 s, summarizes the developed theory and technologies of carbonate reservoir development, analyzes their adaptability and problems, and proposes their development trend. The following theory and technologies have come into being:(1) carbonate reservoir formation mechanisms and compound flow mechanisms in complex medium;(2) reservoir identification and description technologies based on geophysics and discrete fracture-vuggy modeling method;(3) well testing analysis technology and numerical simulation method of coupling free flow and porous media flow;(4) enhanced oil recovery techniques for nitrogen single well huff and puff, and water flooding development techniques with well pattern design in spatial structure, changed intensity water injection, water plugging and channel blocking as the core;(5) drilling and completion techniques, acid fracturing techniques and its production increasing techniques. To realize the efficient development of carbonate oil and gas reservoirs, researches in four aspects need to be done:(1) complex reservoir description technology with higher accuracy;(2) various enhanced oil recovery techniques;(3) improving the drilling method and acid fracturing method for ultra-deep carbonate reservoir and significantly cutting engineering cost;(4) strengthening the technological integration of information, big data, cloud computation, and artificial intelligence in oilfield development to realize the smart development of oilfield.