Accumulation conditions and key technologies for exploration and development of Qinshui coalbed methane field

The Qinshui Basin has been explored for more than 60 years through two stages of oil and gas reconnaissance survey and exploration&development of coalbed methane(CBM),it has become the largest CBM industrialization base in China and also is a model which successfully realize commercialization of CBM of high rank coal-bearing basin in the world.Although the high-rank coal field is characterized by low pressure,low permeability,low saturation and strong heterogeneity,the exploration practice and research show that the accumulation conditions of CBM reservoir in the Qinshui Basin are superior.As main productive intervals,No.15 coal seam of Taiyuan Formation and No.3 coal seam of Shanxi Formation respectively belong to the epicontinental-sea carbonate platform sedimentary system and the epicontinental-sea shallow-water delta sedimentary system.The coal seam has large thickness,and is mostly composed of humic coal and mainly contains vitrinite.Affected by tectonic thermal events in the Yanshanian period,the coal rank is high,the adsorption capacity is strong,and the gas content is large.Formation of the CBM reservoir goes through three stages including two stages of hydrocarbon generation,gas phase transformation and sealing of hydrodynamics and roof and floor.In view of the characteristics of the Qinshui Basin topography and the high rank coal,a series of key technologies for exploration and development are developed,including mountainous region seismic acquisition,processing and interpretation technology,drilling and completion technology of multiple wells,drilling and completion technology of multiple horizontal wells dominated by compound V type,deplugging secondary fracturing stimulation technology,control technology of high rank CBM drainage,and CBM gathering and transportation technology,which effectively supports the scale and industrialization development of high rank CBM in the Qinshui Basin.

Gas accumulation conditions and key technologies for exploration & development of Sinian and Cambrian gas reservoirs in Anyue gasfield

Exploration of the Sinian-Lower Paleozoic formations in the Sichuan Basin starts from the 1950s,and is tortuous and complex.To summarize the exploration experiences is of great significance of reference for exploration of oil and gas in deep carbonate rocks of the Sichuan Basin.Gas accumulation in the Anyue oversize gasfield is chiefly controlled by the Deyang-Anyue intra-platform rift and central Sichuan paleouplift.The intra-platform rift controls the scale hydrocarbon generation center and effective hydrocarbon plays.The Anyue gasfield is characterized by near-source hydrocarbon accumulation.The marginal zone of intra-platform rift and high part of the paleouplift control the scale distribution of favorable facies belts of reservoir development,and overlapped by paleokarstic reformation,the reservoirs are widely distributed.The intra-platform rift and paleouplift jointly control formation of the scale traps and hydrocarbon enrichment.Gas reservoir features and major controlling factors for hydrocarbon accumulation have some differences in the main play strata,such as Longwangmiao Formation,and Member 4 and Member 2 of Dengying Formation.The gas reservoir in the Longwangmiao Formation is a lithologic gas reservoir under the tectonic setting,and the inherited paleouplift is a key for reservoir formation and hydrocarbon accumulation.The gas reservoir in the Member 4 of Dengying Formation is mainly controlled by large structural-stratigraphic composite traps,and the gas reservoir in the Member 2 of Dengying Formation is the structural trap.Distribution of the large gasfields in the Dengying Formation is controlled by the intra-platform rift,near-source hydrocarbon-reservoir configuration controlled by the ancient erosion plane and stratigraphic sealing in the updip direction.For exploration and development of the Anyue gasfield,four series of technologies are developed,namely,reservoir seismic fine description technology,well logging fine evaluation technology of gas layers,fast drilling technology of complex strata,and stimulation technology for high temperature and high pressure gas layers.Technical progresses provide powerful guarantee for efficient exploration and development of the oversize gasfields.

Reservoir formation conditions and key technologies for exploration and development in Qingcheng large oilfield

The Qingcheng oilfield,the largest shale oil field in China,was discovered in 2019 in source rock of Chang 7 Member of Mesozoic Yanchang Formation,Changqing Oilfield in Ordos Basin,with newly increased proven geological reserves of 358 million tons,predicted geological reserves of 693 million tons,and a total of 1.051 billion tons of shale oil resources.This achieves a historic breakthrough in exploration of shale oil in Chang 7 Member.In recent years,focusing on key issues,such as whether there develop sweet spots in source rock,whether commercial oil production capacity can be formed,and whether scale-effective development can be achieved,studies about geological conditions for shale oil accumulation have been continuously carried out,key supporting technologies have been developed,and a series of theoretical innovations and technological breakthroughs have been achieved in oil exploration in source rocks.The results indicate that shale oil accumulation in Chang 7 Member is controlled by following factors.Firstly,lacustrine black shale,dark mudstone and other high-quality source rocks lay a material foundation for shale oil formation.Secondly,sandy deposits intercalated within black shale and dark mudstones are exploration sweet spots,and sandbody combination types are controlled by morphology of bottom of the lacustrine basin.Thirdly,reservoir properties are good due to development of micro-nano pore throats.Finally,reservoirs with high oil saturation and high gas-oil ratio are formed due to high-intensity oil charging in source rock.Effective matching of multiple factors is a key for shale oil accumulation in Chang 7 Member in Ordos Basin.Through innovation of key supporting technologies,exploration and development technologies for shale oil are developed,and substantial breakthrough on exploration and development of shale oil is realized.The first application of logging-seismic combination technology in loess plateau improves significantly quality of 3D seismic data,which effectively guides prediction of sandy sweet spots.Three-quality well logging technology is used for further evaluation of geological and engineering sweet spots of shale oil.With volumetric fracturing technology based on precise segmentation of long horizontal wells,initial daily oil production of individual well is increased from previously 10 tons to more than 18 tons.The exploration breakthrough in source rocks in Chang 7 Member in Qingcheng oilfield provides an important resource base for the second accelerated development of Changqing Oilfield.It is predicated that oil production from shale in Chang 7 Member in Qingcheng oilfield will reach three million tons in 2022 and five million tons in 2025.