Influence of reservoir heterogeneity on immiscible water-alternating-CO_(2)flooding:A case study

Currently,limited studies of immiscible water-alternating-CO_(2)(imWACO_(2))flooding focus on the impact of reservoir heterogeneity on reservoir development outcomes.Given this,using the heterogeneous reservoirs in the Gao 89-1 block as a case study,this study conducted slab core flooding experiments and numerical simulations to assess the impact of reservoir heterogeneity on imWACO_(2)flooding efficiency.It can be concluded that imWACO_(2)flooding can enhance the sweep volume and oil recovery compared to continuous CO_(2)flooding.As the permeability difference increases,the difference in the swept volume between zones/layers with relatively high and low permeability increases.To optimize the exploitation of reservoirs in the Gao 89-1 block,the optimal timing and CO_(2)injection rate for imWACO_(2)flooding are determined at water cut of 40%and 10000 m^(3)/d,respectively.A short injection-production semi-period,combined with multiple cycles of water and CO_(2)injection alternations,is beneficial for enhanced oil recovery from imWACO_(2)flooding.

A novel responsive stabilizing Janus nanosilica as a nanoplugging agent in water-based drilling fluids for exploiting hostile shale environments

Thermo-responsive nanocomposites have recently emerged as potential nanoplugging agents for shale stabilization in high-temperature water-based drilling fluids(WBDFs). However, their inhibitory properties have not been very effective in high-temperature drilling operations. Thermo-responsive Janus nanocomposites are expected to strongly interact with clay particles from the inward hemisphere of nanomaterials, which drive the establishment of a tighter hydrophobic membrane over the shale surface at the outward hemisphere under geothermal conditions for shale stabilization. This work combines the synergistic benefits of thermo-responsive and zwitterionic nanomaterials to synchronously enhance the chemical inhibitions and plugging performances in shale under harsh conditions. A novel thermoresponsive Janus nanosilica(TRJS) exhibiting zwitterionic character was synthesized, characterized,and assessed as shale stabilizer for WBDFs at high temperatures. Compared to pristine nanosilica(Si NP)and symmetrical thermo-responsive nanosilica(TRS), TRJS exhibited anti-polyelectrolyte behaviour, in which electrolyte ions screened the electrostatic attraction between the charged particles, potentially stabilizing nanomaterial in hostile shaly environments(i.e., up to saturated brine or API brine). Macroscopically, TRJS exhibited higher chemical inhibition than Si NP and TRS in brine, prompting a better capability to control pressure penetration. TRJS adsorbed onto the clay surface via chemisorption and hydrogen bonding, and the interactions became substantial in brine, according to the results of electrophoretic mobility, surface wettability, and X-ray diffraction. Thus, contributing to the firm trapping of TRJS into the nanopore structure of the shale, triggering the formation of a tight hydrophobic membrane over the shale surface from the outward hemisphere. The addition of TRJS into WBDF had no deleterious effect on fluid properties after hot-treatment at 190℃, implying that TRJS could find potential use as a shale stabilizer in WBDFs in hostile environments.

Organic geochemical,petrographic and palynological characterization of claystones of the Palaeogene Toraja Formation,and oil seeps in the Enrekang Sub-basin,south Sulawesi,Indonesia:Implications for hydrocarbon source rock potential

An organic geochemical,petrographical,and palynological evaluation was conducted on 30 claystone outcrop samples of the Toraja Formation,along with a geochemical analysis of an oil seep in the Enrekang Sub-basin.The aim of the study was to determine the correlation between oil and source rock in terms of age,depositional environment,organic material sources,and maturity level.The total organic carbon content of the claystone samples varies from 0.03 to 4.52 wt%,which are classified as poor to excellent.The claystones are immature to post-mature with a mixture of TypeⅡandⅢkerogen.Their vitrinite reflectance values range from 0.47 to 4.52%Ro.The samples of Toraja Formation rock and the oil seep source rock might have a similar depositional environment,a deltaic marine depositional setting with high oxidizing conditions.Organic material sources for rock and oil samples are dominated by terrestrial input.The oil is inferred to have originated from the Paleogene source rocks,which correlates in age with the Toraja Formation.The recovered palynomorphs from the studied rock samples suggest a late Eocene to Oligocene age with a strong terrestrial influence of shallow marine depositional setting.The biomarker analysis shows that the rock samples have a more substantial contribution from the terrigenous higher plants,while the oil sample indicates a higher degree of marine influence.The maturity levels are also different between the oil(peak mature)and the analyzed rock samples(immature).It is inferred that the oil seep source rock is equivalent to the analyzed rock sample but more mature,having been deposited under more marine conditions.The oil seep source rock is not exposed and is located in the deeper part of the basin.A deeper marine facies(i.e.distal delta front and prodelta facies)in front of the distributary mouth bar within a delta is interpreted as the source rock of the oil seep sample.

The deposition of asphaltenes under high-temperature and highpressure (HTHP) conditions

In this work,the factors affecting asphaltenes deposition in high-temperature and high-pressure wells were studied using backscattered light and PVT equipment customized to suit the well conditions.In an examination of the intensity of backscattered light,it was revealed that there exists a linear relationship between temperature and asphaltene precipitation within a specific temperature range.Within this range,a decrease in temperature tends to accelerate asphaltene precipitation.However,the impacts of pressure and gas-oil ratio are more pronounced.The pressure depletion induces the asphaltenes to precipitate out of the solution,followed by the formation of flocs below the bubble point.In addition,an increase in the gas-oil ratio causes a more severe asphaltene deposition,shifting the location of asphaltenes to deep well sections.

Anomaly detection on displacement rates and deformation pattern features using tree-based algorithm in Japan and Indonesia

Research on strain anomalies and large earthquakes based on temporal and spatial crustal activities has been rapidly growing due to data availability, especially in Japan and Indonesia. However, many research works used local-scale case studies that focused on a specific earthquake characteristic using knowledgedriven techniques, such as crustal deformation analysis. In this study, a data-driven-based analysis is used to detect anomalies using displacement rates and deformation pattern features extracted from daily global navigation satellite system(GNSS) data using a machine learning algorithm. The GNSS data with188 and 1181 continuously operating reference stations from Indonesia and Japan, respectively, are used to identify the anomaly of recent major earthquakes in the last two decades. Feature displacement rates and deformation patterns are processed in several window times with 2560 experiment scenarios to produce the best detection using tree-based algorithms. Tree-based algorithms with a single estimator(decision tree), ensemble bagging(bagging, random forest and Extra Trees), and ensemble boosting(AdaBoost, gradient boosting, LGBM, and XGB) are applied in the study. The experiment test using realtime scenario GNSSdailydatareveals high F1-scores and accuracy for anomaly detection using slope windowing 365 and 730 days of 91-day displacement rates and then 7-day deformation pattern features in tree-based algorithms. The results show the potential for medium-term anomaly detection using GNSS data without the need for multiple vulnerability assessments.

Comprehensive evaluation of chemical breakers for multistage network ultra-high strength gel

Polymer gels have been accepted as a useful tool to address many sealing operations such as drilling and completion,well stimulation,wellbore integrity,water and gas shutoff,etc.Previously,we developed an ultra-high strength gel(USGel)for medium to ultra-low temperature reservoirs.However,the removal of USGel is a difficult problem for most temporary plugging operations.This paper first provides new insights into the mechanism of USGel,where multistage network structure and physical entanglement are the main reasons for USGel possessing ultra-high strength.Then the effects of acid breakers,encapsulated breakers,and oxidation breakers(including H_(2)O_(2),Na_(2)S_(2)O_(8),Ca(ClO)_(2),H_(2)O_(2)+NaOH,Na_(2)S_(2)O_(8)+NaOH,and Ca(ClO)_(2)+NaOH)were evaluated.The effects of component concentration and temperature on the breaking solution were studied,and the corrosion performance,physical simulation and formation damage tests of the breaking solution were carried out.The final formulation of 2%-4%NaOH+4.5%-6%H_(2)O_(2) breaking solution was determined,which can make USGel completely turn into water at 35e105C.The combinations of“acid t breaking solution”,“acid+encapsulated breaker”and“encapsulated breaker+breaking solution”were evaluated for breaking effect.The acid gradually reduced the volume of USGel,which increased the contact area between breaking solution and USGel,and the effect of“4%acid+breaking solution”was 23 times higher than that of breaking solution alone at 35C.However,the acid significantly reduced the strength of USGel.This paper provides new insights into the breaking of high-strength gels with complex network structures.

A Dynamic Plunger Lift Model for Shale Gas Wells

At present,the optimization of the plunger mechanism is shale gas wells is mostly based on empirical methods,which lack a relevant rationale and often are not able to deal with the quick variations experienced by the production parameters of shale gas wells in comparison to conventional gas wells.In order to mitigate this issue,in the present work,a model is proposed to loosely couple the dynamics of gas inflow into shale gas wells with the dynamics of the liquid inflow.Starting from the flow law that accounts for the four stages of movement of the plunger,a dynamic model of the plunger lift based on the real wellbore trajectory is introduced.The model is then tested against 5 example wells,and it is shown that the accuracy level is higher than 90%.The well‘switch’,optimized on the basis of simulations based on such a model,is tested through on-site experiments.It is shown that,compared with the original switch configuration,the average production of the sample well can be increased by about 15%.

Pressure Buildup Analysis for a Well in a Closed, Bounded Multiwell Reservoir

A general method has been developed for analyzing pressure buildup data from a well located in a system with both production and injection wells in a closed, bounded two-phase flow reservoir. The proposed method enables one to calculate the total mobility or permeability-thickness product, the skin factor, the average drainage-area pressure and the injection-production ratio （at the instant of shut-in） with accuracy from pressure buildup （or falloff） data dominated by a linear trend of reservoir pressure. Out of thousands of well tests, several typical field examples have been presented to illustrate the application of the proposed method for analyzing pressure transient data from a well located in a water-injection multiwell reservoir. And the possible application of this method to heterogeneous systems such as naturally fractured reservoirs is also discussed. Approaches to aid practicing engineers in verifying the buildup interpretation （or recognizing the interference of offset wells） are presented. Extension of the presented method to a gas well located in a multiwell gas reservoir is also suggested

Effect of AMPS(2-acrylamido-2-methylpropane sulfonic acid) content on the properties of polymer gels

The BST oilfield in the northwestern Taklamakan Desert is a fractured carbonate reservoir,but issues of water breakthrough are becoming increasingly severe with the development of water flooding.Unfortunately,the high-temperature and high-salt conditions(130°C,71695 mg/L)of the BST oilfield pose challenges for the development of plugging agents.In this study,the effects of 2-acrylamido-2-methylpropane sulfonic acid(AMPS)content on AM/AMPS copolymers and gels were studied through viscosity measurements,nuclear magnetic resonance(NMR),and cryo-scanning electron microscope(Cryo-SEM).Moreover,the AMPS stabilization mechanism of the polymers and gels was explained.Heatresistant and salt-tolerant gel systems were developed,and their gelation properties,thermal stability,injection capacity,and plugging ability were evaluated.Experimental results showed inconsistencies between the effects of AMPS content on the polymers and gels.For the polymers,the thermal stability increased with increased AMPS content in the polymer.However,excessive AMPS content resulted in poor gelation and low strength.The developed gel systems with S30 polymer(AMPS content is approximately 26%)exhibited excellent thermal stability,controllable gelation time,good injection capacity,and plugging ability.The field application results indicated that most production wells had a positive response,with reduced water-cut and increased daily oil production.

Slug Flow Characteristics in Inclined and Vertical Channels

Horizontal well production technology gradually occupies a dominant position in the petroleum field.With the rise in water production in the later stage of exploitation,slug flow phenomena will exist in horizontal,inclined and even vertical sections of gas wells.To grasp the flow law of slug flow and guide engineering practice,the flow law of slug flow at various inclination angles(30°~90°)is studied by means of the combination of laboratory experiments(including high frequency pressure data acquisition system)and finite element numerical simulation.The results reveal that because of the delay of pressure variation at the corresponding position of pipeline resulting from gas expansion,the highest point of pressure change curve corresponds not to the highest point of liquid holdup curve(pressure change lags behind 0.125 s of liquid holdup change).Thus,the delay of pressure should be highlighted in predicting slug flow using pressure parameter change;otherwise the accuracy of prediction will be affected when slug flow occurs.It is generally known that liquid holdup and pressure drop are the major factors affecting the pressure variation and stable operation of pipelines.Accordingly,the results of finite element numerical simulation and Beggs-Brill model calculation are compared with those of laboratory experiments.The numerical simulation method is applicable to predicting the pressure drop of the pipeline,while the Beggs-Brill model is more suitable for predicting the liquid holdup variation of the pipeline.The research conclusion helps reveal the slug flow law,and it is of a scientific guiding implication to the prediction method of flow parameters under slug flow pattern in the process of gas well exploitation.

Flow Simulation of a Horizontal Well with Two Types of Completions in the Frame of a Wellbore–Annulus–Reservoir Model

Well completions are generally used to connect a reservoir to the surface so that fluids can be produced from orinjected into it. With these systems, pipe flows are typically established in the horizontal sections of slotted screencompletions and inflow control device (ICD) completions;moreover, an annular flow exists in the region betweenthe pipe and the borehole wall. On the basis of the principles of mass and momentum conservation, in the presentstudy, a coupling model considering the variable mass flow of the central tubing, the variable mass flow of theannular tubing and the reservoir seepage is implemented to simulate the wellbore–annulus–reservoir behaviorin the horizontal section of slotted-screen and ICD completions. In earlier models, only the central tubing variablemass flow and reservoir seepage flow were considered. The present results show that the closer the heel end, thegreater is the flow per unit length in the central tubing from the annulus. When external casing packers are notconsidered, the predicted production rate of the slotted screen completion, which is obtained using the variablemass flow model not taking into account the annulus flow, is 9.51% higher than the rate obtained using the (complete) model with annulus flow. In addition, the incomplete model forecasts the production of ICD completion ata 70.98% higher rate. Both models show that the pressure profile and flow profile of the borehole wall are relatively uniform in the wellbore–annulus–reservoir in horizontal wells.

Study on a Gas Plunger Lift Model for Shale Gas Wells and Its Effective Application

The problem of efficient gas lift for gas well annulus packers that rely on their own energy plungers is considered.The complex related gas-liquid problem is addressed in the frame of model where the gas inflow dynamics and liquid inflow dynamics of the considered shale gas wells are weakly coupled.On this basis,and with the aiding support of indoor simulation experimental data,a new gas plunger lift design taking into account liquid leakage is obtained.Finally,a dedicated software relying on this approach is developed and used to verify the reliability of the model by means of field examples.

Analysis of explosion risk factor potential on coal reclaim tunnel facilities by modified analytical hierarchy process

This study focused on developing a risk assessment method for explosion at a coal reclaim tunnel （CRT） facility. The method was developed based on an analytical hierarchy process （AHP）, which is an expert system that quantifies the factors of explosion incidents, based on events and hierarchies. In this paper, the proposed model was modification from original AHP model, specifically modifying the structure from ＂alternative＇s results＂ to ＂total risk-rating＇s results＂. The total risk-rating is obtained by summing up risk-rating of each factor, where the risk-rating is a multiplication product of the risk value by the AHP weighted value. To support decision-making using the expert system, data on the real conditions of the CRT were collected and analyzed. A physical modeling of the CRT with laboratory-scale experiments was carried out to show the impact of a ventilation system in CRT on diluting the methane gas and coal dust, in order to support the quantification of AHP risk value. The criteria to evaluate the risk of explosion was constructed from six components that are： fuel, oxygen, ignition, confinement, dispersion, and monitoring system. Those components had fifty-two factors that serve as sub-components （root causes）. The main causes of explosion in CRT were found to be： mechanical ventilation failure and abnormal ventilation, breakdown of monitoring system, and coal spontaneous-combustion. Assessments of two CRT facilities at Mine A and Mine B were carried out as a case study in order to check the reliability of the developed AHP method. The results showed that the risk rating of Mine A was classified as high and Mine B was classified as medium, which is in a good agreement with the site conditions.

Dissolution of lateritic nickel ore using ascorbic acid as synergistic reagent in sulphuric acid solution

The dissolution of nickel and cobalt from Caldag lateritic nickel ore using the combination of sulphuric and ascorbic acids was investigated. The use of other organic acids, namely citric, maleic and stearic acids, as synergistic reagents was studied for comparison. The results revealed that the use of ascorbic and citric acids markedly improved the dissolution of cobalt compared to the other two organic acids that only showed slight synergistic effect on the leaching rate. In terms of nickel dissolution, ascorbic acid is the most effective synergist, followed by citric, maleic and stearic acids in descending order. Under the most optimized conditions found in this study, i.e., using 1 mol/L of sulphuric acid with the presence of 4 g/L of ascorbic acid at 80 ℃and solid-to-liquid ratio of 1/10, more than 99% and 98% leaching rates of cobalt and nickel, respectively, can be achieved within 4 h of leaching. In addition, the leaching performance is relatively insensitive to the change of ascorbic acid concentration from 2 to 4 g/L which is highly desirable from operational perspective.

Dynamic characteristics and influencing factors of CO_(2) huff and puff in tight oil reservoirs

CO_(2)huff and puff experiments of different injection parameters,production parameters and soaking time were carried out on large-scale cubic and long columnar outcrop samples to analyze dynamic characteristics and influencing factors of CO_(2)huff and puff and the contribution of sweeping mode to recovery.The experimental results show that the development process of CO_(2)huff and puff can be divided into four stages,namely,CO_(2)backflow,production of gas with some oil,high-speed oil production,and oil production rate decline stages.The production of gas with some oil stage is dominated by free gas displacement,and the high-speed oil production stage is dominated by dissolved gas displacement.CO_(2)injection volume and development speed are the major factors affecting the oil recovery.The larger the injected CO_(2)volume and the lower the development speed,the higher the oil recovery will be.The reasonable CO_(2)injection volume and development speed should be worked out according to oilfield demand and economic evaluation.There is a reasonable soaking time in CO_(2)huff and puff.Longer soaking time than the optimum time makes little contribution to oil recovery.In field applications,the stability of bottom hole pressure is important to judge whether the soaking time is sufficient during the huff period.The oil recovery of CO_(2)huff and puff mainly comes from the contribution of flow sweep and diffusion sweep,and diffusion sweep contributes more to the oil recovery when the soaking time is sufficient.

Numerical simulation to evaluate gas diffusion of turbulent flow in mine ventilation system

Tracer gas technique is a method to analyze the airflow path, measure the airflow quantity, and detect any recirculation or leakages in underground mine. In addition, it is also possible to evaluate the axial gas diffusion of gas in turbulent bulk flow by utilizing the tracer gas data. This paper discussed about the measurement using tracer gas technique in Cibaliung Underground Mine, Indonesia and the evaluation of effective axial diffusion coefficient, E, by numerical simulation. In addition, a scheme to treat network flow in mine ventilation system was also proposed. The effective axial diffusion coefficient for each airway was evaluated based on Taylor's theoretical equation. It is found that the evaluated diffusion coefficient agrees well with Taylor's equation by considering that the wall friction factor, f, is higher than those for smooth pipe flow. It also shows that the value of effective diffusion coefficient can be inherently determined and the value is constant when matching with other measurements. Furthermore, there are possibilities to utilize the tracer gas measurement data to evaluate the airway friction factors.

Effects of Anodizing Parameters in Tartaric-Sulphuric Acid on Coating Thickness and Corrosion Resistance of Al 2024 T3 Alloy

2024 T3 is one of aluminium alloys which are widely used in the aircraft structures. Anodizing of alluminium alloy in tartaric-sulphuric acid (TSA) electrolyte is developed to obtain more environmentally-friendly process and to produce anodize layer with better corrosion resistance. In this research work, the influences of anodizing parameters of Al 2024 T3 in TSA on the thickness, weight and corrosion resistance of the anodize layer are studied. Corrosion resistance test was carried out by conducting salt spray test for 336 hours and anodic polarization measurements using potentiostat. Results of three-factor analysis of variance (ANOVA) demonstrated that the most influencing factor that determines the thickness and weight of the anodize layer is temperature, followed by applied voltage, duration of anodizing, voltage-temperature interaction, interaction of temperature-duration of anodizing, interaction of voltage-temperature-duration of anodizing, and interaction of voltage and duration of anodizing. The pit density and corrosion current density (icorr) were found to be dependent on the coating thickness. The anodize layer with a thickness of higher than 3 μm was not experienced to pitting corrosion during 336 hours of salt spray test.

Preparation and stabilization mechanism of carbon dots nanofluids for drag reduction

During the development of low or ultra-low permeability oil resources,the alternative energy supply becomes a prominent issue.In recent years,carbon dots(CDs)have drawn much attention owing to their application potential in oil fields for reducing injection pressure and augmenting oil recovery.However,carbon dots characterized of small size,high surface energy are faced with several challenges,such as self-aggregation and settling.The preparation of stably dispersed carbon dots nanofluids is the key factor to guarantee its application performance in formation.In this work,we investigated the stability of hydrophilic carbon dots(HICDs)and hydrophobic carbon dots-Tween 80(HOCDs)nanofluids.The influences of carbon dots concentration,sorts and concentration of salt ions as well as temperature on the stability of CDs were studied.The results showed that HICDs are more sensitive to sort and concentration of salt ions,while HOCDs are more sensitive to temperature.In addition,the core flooding experiments demonstrated that the pressure reduction rate of HICDs and HOCDs nanofluids can be as high as 17.88%and 26.14%,respectively.Hence,the HICDs and HOCDs nanofluids show a good application potential in the reduction of injection pressure during the development of low and ultra-low permeability oil resources.

CFD analysis and field observation of tool erosion caused by abrasive waterjet fracturing

Abrasive waterjet(AWJ)fracturing has become an accepted horizontal multistage stimulation technique due to its flexibility and high efficiency of extensive fracture placement.The downhole tool failure of AWJ fracturing becomes an issue in the massive hydraulic fracturing because of high velocity and proppant erosion.This paper proposed a 3D computational fluid dynamics(CFD)-based erosion model by considering high-velocity waterjet impact,proppant shear erosion,and specific inner structure of hydra-jet tool body.The discrete phase approach was used to track the proppant transport and its concentration distribution.Field observation provides strong evidence of erosion patterns and mechanisms obtained from CFD simulation.The results show that the erosion rate has a space dependence in the inner wall of the tool body.The severe erosion areas are primarily located at the entries of the nozzle.Evident erosion patterns are found including a‘Rabbit’s ear’erosion at the upper-layer nozzles and a half bottom loop erosion at the lower-layer nozzles.Erosion mechanisms attribute to high flow velocity at the entry of nozzles and the inertia force of proppant.Sensitivity analysis demonstrates that the pumping rate is a primary factor contributing to erosion intensity.

Mechanisms of shale hydration and water block removal

Shale samples of Silurian Longmaxi Formation in the Changning area of the Sichuan Basin, SW China, were selected to carry out scanning electron microscopy, CT imaging, high-pressure mercury injection, low-temperature nitrogen adsorption and imbibition experiments to compare the hydration characteristics of montmorillonite and illite, analyze the main factors affecting the water block removal of shale, and reveal the mechanisms of pore structure evolution during shale hydration. The hydration characteristics of shale are closely related to the composition of clay minerals, the shale with high illite content is not susceptible to hydration and thus has limited room for pore structure improvement;the shale with high montmorillonite is susceptible to hydration expansion and thus has higher potential of pore structure improvement by stimulation;the shale with high illite content has stronger imbibition in the initial stage, but insufficient diffusion ability, and thus is likely to have water block;the shale with high montmorillonite content has weaker imbibition in the initial stage but better water diffusion, so water blocking in this kind of shale can be removed to some degree;the shale reservoir has an optimal hydration time, when it is best in physical properties, but hydration time too long would cause damage to the reservoir, and the shale with high illite content has a shorter optimal hydration time;inorganic cations can inhibit the hydration of clay minerals and have stronger inhibition to illite expansion, especially K^(+);for the reservoir with high content of montmorillonite, the cation content of fracturing fluid can be lowered to promote the shale hydration;fracturing fluid with high K^(+) content can be injected into reservoirs with high illite content to suppress hydration.