Comprehensive comparison and development strategy suggestions between the edge and interior of the fourth section of the Sinian series lamps in the Gaoshiti block

HU Hao; WANG Min; LONG Hui; JIANG Lin; SHEN Qiuyuan; WU Dong; TIAN Xingwang

doi:10.11932/karst20250217

Abstract：The fourth section of Dengying Formation in the Gaoshiti block of the Anyue Gas Field is of complex lithology and strong heterogeneity.There is a significant difference in the single-well production capacity as well as in production efficiency between the platform margin and the intra-platform.To achieve long-term stable development of the gas reservoir in the fourth section of Dengying Formation at the platform margin,as well as efficient production of the corresponding section in the intra-platform,the controlling factors leading to the observed differences have been identified.This was accomplished through a combination of dynamic and static methods,which allowed for a comprehensive analysis of the common and distinct characteristics of the gas reservoirs in both the platform margin and intra-platform.This analysis was based on a substantial amount of geological,logging,gas reservoir engineering and other relevant data. The reservoir rock types and reservoir space in both the platform margin and the intra-platform share common characteristics.The lithology is primarily composed of doloarenite,algal-laminated dolomite,and algal-clotted dolomite.These rocks are all well developed in terms of dissolution pores.The porosity of the reservoir core ranges from 2.0％to 7.3％,with an average of 3.5％.The permeability ranges from 0.1 mD to 113 mD,with an average of 5.832 mD.The reservoir properties exhibit low porosity and low permeability,and the reservoir type is primarily characterized as fracture-pore(cave)type. However,there are differences between the platform margin and the intra-platform in terms of reservoir development scale,degree of dissolution pore development,reservoir physical properties,seepage characteristics,and characteristics of gas well production.At the platform margin,the proportion of wells with single-well test output larger than 500,000 cubic meters of gas is higher.The development degree of large pores and caves is greater,and the density of fracture development is also higher.In terms of production,the gas wells at the platform margin generally exhibit high and stable production,with an average daily gas production of 233,000 cubic meters per well.In contrast,the gas wells in the intra-platform show significant production differences,with a daily gas production of 145,000 cubic meters.In terms of seepage characteristics,the reservoir type at the platform margin is primarily classified as fracture-pore type,with fractures and fracture-cave systems serving as the main seepage channels.These wells exhibit relatively high test production rates and are capable of maintaining high and stable production. This paper comprehensively analyzes the reasons for the differences from four aspects,sedimentary environment,diagenesis,matching of reservoir conditions,and karst transformation.It clarifies that the sedimentary environment and reservoir conditions control the scale of reservoir development,while karst transformation in later stages plays a decisive role in the seepage characteristics and production differences of gas wells.The favorable shoal and lagoon bodies control the distribution of high-quality reservoirs,and the intensity of epigenetic karst transformation during the Tongwan Period determines the strength of dissolution and transformation.Additionally,the relationship between source and reservoir affects the efficiency of hydrocarbon migration and accumulation.Therefore,the development scale of shoal and lagoon deposits,the intensity of epigenetic karst transformation,and the source-reservoir relationship are the primary controlling factors determining the differences between the platform margin and the intra-platform. Based on a comprehensive comparison between the platform margin and the intra-platform,the former exhibits the thicker reservoir,superior physical properties,and dominant storage space types characterized by fracture-pore(cave)patterns.It also features a larger controlled radius,better fluid flow,a higher proportion of high-yield wells,and the potential for long-term,stable high production.In contrast,the intra-platform has the relatively thinner reservoir,comparable physical properties,and greater horizontal heterogeneity,resulting in more significant differences in the development of high-quality reservoirs.The production capacity of gas wells primarily comes from medium-and-low-yield wells,with a smaller proportion of wells capable of stable production.Given this comparison between the two zones and the production and development needs of the Gaoshiti block,the differentiated production suggestions are proposed.For the platform margin,the detailed characterization of high-quality seepage bodies within reservoir should be conducted,and the development of supplementary wells should be implemented to achieve stable production of gas reservoirs.For the intra-platform,the identification of favorable site distributions should be prioritized,and the production wells should be deployed to ensure efficient production.