Deep-water gravity flow deposits in a lacustrine rift basin and their oil and gas geological significance in eastern China

The types,evolution processes,formation mechanisms,and depositional models of deep-water gravity flow deposits in a lacustrine rift basin are studied through core observation and systematic analysis.Massive transport of slide and slump,fluid transport of debris flow and turbidity currents are driven by gravity in deep-water lacustrine environment.The transformation between debris flow and turbidity current,and the transformation of turbidity current between supercritical and subcritical conditions are the main dynamic mechanisms of gravity flow deposits in a lake basin.The erosion of supercritical turbidity current controls the formation of gravity-flow channel.Debris flow deposition gives rise to tongue shape lobe rather than channel.Deep-water gravity flow deposits are of two origins,intrabasinal and extrabasinal.Intrabasinal gravity flow deposits occur as single tongue-shape lobe or fan of stacking multiple lobes.Extrabasinal gravity-flow deposits occur as sublacustrine fan with channel or single channel sand body.However,the nearshore subaqueous fan is characterized by fan of stacking multiple tongue shape lobes without channel.The differential diagenesis caused by differentiation in the nearshore subaqueous fan facies belt results in the formation of diagenetic trap.The extrabasinal gravity flow deposits are one of the important reasons for the abundant deep-water sand bodies in a lake basin.Slide mass-transport deposits form a very important type of lithologic trap near the delta front often ignored.The fine-grained sediment caused by flow transformation is the potential"sweet spot"of shale oil and gas.

Stability analysis of seabed strata and casing structure during the natural gas hydrates exploitation by depressurization in horizontal wells in South China Sea

Natural gas hydrates(NGHs)are a new type of clean energy with great development potential.However,it is urgent to achieve safe and economical NGHs development and utilization.This study established a physical model of the study area using the FLAC^(3D) software based on the key parameters of the NGHs production test area in the South China Sea,including the depressurization method,and mechanical parameters of strata,NGHs occurrence characteristics,and the technological characteristics of horizontal wells.Moreover,this study explored the law of influences of the NGHs dissociation range on the stability of the overburden strata and the casing structure of a horizontal well.The results are as follows.With the dissociation of NGHs,the overburden strata of the NGHs dissociation zone subsided and formed funnelshaped zones and then gradually stabilized.However,the upper interface of the NGHs dissociation zone showed significant redistribution and discontinuity of stress.Specifically,distinct stress concentration and corresponding large deformation occurred in the build-up section of the horizontal well,which was thus prone to suffering shear failure.Moreover,apparent end effects occurred at the end of the horizontal well section and might cause the deformation and failure of the casing structure.Therefore,it is necessary to take measures in the build-up section and at the end of the horizontal section of the horizontal well to prevent damage and ensure the wellbore safety in the long-term NGHs exploitation.

Theoretical Progress and Key Technologies of Onshore Ultra-Deep Oil/Gas Exploration

Oil/gas exploration around the world has extended into deep and ultra-deep strata because it is increasingly difficult to find new large-scale oil/gas reservoirs in shallow–middle buried strata. In recent years, China has made remarkable achievements in oil/gas exploration in ultra-deep areas including carbonate and clastic reservoirs. Some (ultra) large-scale oil and gas fields have been discovered. The oil/gas accumulation mechanisms and key technologies of oil/gas reservoir exploration and development are summarized in this study in order to share China’s experiences. Ultra-deep oil/gas originates from numerous sources of hydrocarbons and multiphase charging. Liquid hydrocarbons can form in ultradeep layers due to low geothermal gradients or overpressures, and the natural gas composition in ultra-deep areas is complicated by the reactions between deep hydrocarbons, water, and rock or by the addition of mantle- or crust-sourced gases. These oils/gases are mainly stored in the original highenergy reef/shoal complexes or in sand body sediments. They usually have high original porosity. Secondary pores are often developed by dissolution, dolomitization, and fracturing in the late stage. The early pores have been preserved by retentive diageneses such as the early charging of hydrocarbons. Oil/gas accumulation in ultra-deep areas generally has the characteristics of near-source accumulation and sustained preservation. The effective exploration and development of ultra-deep oil/gas reservoirs depend on the support of key technologies. Use of the latest technologies such as seismic signal acquisition and processing, low porosity and permeability zone prediction, and gas–water identification has enabled the discovery of ultra-deep oil/gas resources. In addition, advanced technologies for drilling, completion, and oil/gas testing have ensured the effective development of these fields.

The impacts of gas impurities on the minimum miscibility pressure of injected CO_2-rich gas–crude oil systems and enhanced oil recovery potential

An effective parameter in the miscible-CO_2 enhanced oil recovery procedure is the minimum miscibility pressure(MMP)defined as the lowest pressure that the oil in place and the injected gas into reservoir achieve miscibility at a given temperature. Flue gases released from power plants can provide an available source of CO_2,which would otherwise be emitted to the atmosphere, for injection into a reservoir. However, the costs related to gas extraction from flue gases is potentially high. Hence, greater understanding the role of impurities in miscibility characteristics between CO_2 and reservoir fluids helps to establish which impurities are tolerable and which are not. In this study, we simulate the effects of the impurities nitrogen(N_2), methane(C_1), ethane(C_2) and propane(C_3) on CO_2 MMP. The simulation results reveal that,as an impurity, nitrogen increases CO_2–oil MMP more so than methane. On the other hand, increasing the propane(C_3)content can lead to a significant decrease in CO_2 MMP, whereas varying the concentrations of ethane(C_2) does not have a significant effect on the minimum miscibility pressure of reservoir crude oil and CO_2 gas. The novel relationships established are particularly valuable in circumstances where MMP experimental data are not available.

Technological progress and development directions of PetroChina overseas oil and gas field production

This study reviews the development history of PetroChina’s overseas oil and gas field development technologies, summarizes the characteristic technologies developed, and puts forward the development goals and technological development directions of overseas business to overcome the challenges met in overseas oil and gas production. In the course of PetroChina’s overseas oil and gas field production practice of more than 20 years, a series of characteristic technologies suitable for overseas oil and gas fields have been created by combining the domestic mature oil and gas field production technologies with the features of overseas oil and gas reservoirs, represented by the technology for high-speed development and stabilizing oil production and controlling water rise for overseas sandstone oilfields, high efficiency development technology for large carbonate oil and gas reservoirs and foamy oil depletion development technology in use of horizontal wells for extra-heavy oil reservoirs. Based on in-depth analysis of the challenges faced by overseas oil and gas development and technological requirements, combined with the development trends of oil and gas development technologies in China and abroad, overseas oil and gas development technologies in the future are put forward, including artificial intelligence reservoir prediction and 3 D geological modeling, secondary development and enhanced oil recovery(EOR) of overseas sandstone oilfields after high speed development, water and gas injection to improve oil recovery in overseas carbonate oil and gas reservoirs, economic and effective development of overseas unconventional oil and gas reservoirs, efficient development of marine deep-water oil and gas reservoirs. The following goals are expected to be achieved: keep the enhanced oil recovery(EOR) technology for high water-cut sandstone oilfield at international advanced level, and make the development technology for carbonate oil and gas reservoirs reach the international advanced level, and the development technologies for unconventional and marine deep-water oil and gas reservoirs catch up the level of international leading oil companies quickly.

Key technologies, engineering management and important suggestions of shale oil/gas development: Case study of a Duvernay shale project in Western Canada Sedimentary Basin

The Duvernay project in Canada was taken as an example to summarize the advanced technology and engineering management model of shale oil and gas development in North America.Preliminary suggestions were put forward to accelerate the commercial development of domestic continental shale oil and gas.The advanced technologies,valuable knowledge and rich experience were introduced,including the evaluation of geological target area of the project,rapid long horizontal drilling and completion,high-intensity fracturing,and well spacing optimization.In particular,the concept and connotation of the full-life cycle management of North American unconventional resource projects were analyzed.Its emphasis on early evaluation and risk management,and a highly competitive market environment have played an important role in promoting technological innovation and management innovation.In addition,the low-cost sharing system of industry-wide knowledge and experience and the management mode were applied.These management approaches are of great significance for reference in accelerating the exploration and development of unconventional resources in China.China possesses abundant shale oil and gas resources,which are an important replacement to guarantee the national oil and gas energy supply.However,due to the late start and special geological characteristics and engineering difficulties in China,there is a large gap in technology level and management mode compared with North America.According to the advanced experience and enlightenment of the shale oil and gas development in North America,a preliminary proposal to accelerate the development of shale oil and gas in China was made.