Research On Structure Condition Of Coalbed Methane Reservoir Formation

Geological condition in our country is far different from that in U.S.A. which decides the overall condition of CBM enrichment in China. The CBM industrial production region lies in transition zone which is one part of a single continent in U.S.A., but a compound continent that is made up of some small platform, landmass and fold belt in China.Effect of structure on CBM formation and destruction reflects in three aspects: geological developing history, fold and fracture. Region where valid depth is smaller than 200m has no exploration value. CBM is easy to escape over the neutral plane where shows tensile stress in antiform; CBM accumulates under the neutral plane. CBM sealed condition is bad under neutral plane at axial part where shows tensile stress in syncline structure. It is of momentous significance to gas content prediction deeply. The extensional and transtentional structure existed in Huabei belongs to vent fault, fracture is mainly stepwise normal fault, whose preservation condition is not good. The compress and compresso-shear structure distributed in Huanan belongs to barrier fault, which is beneficial for CBM preservation. This paper summaries ten basic tectonic type and similar thirteen kinds of tectonic forms according to different combination of tectonic forms and structure, combined with the characteristic of fault kinematics. Eighteen types are formed in space according to major stress difference of modern structure stress field.In accordance with the main contradictions between high deterioration degree of coal and low permeability of coal bed, this paper predicts high permeability region by use of new technique and methods including stress field, curvature analysis and major stress difference analysis. Studying ancient stress field aimed at predicting cleat-developed zone, studying modern stress field aimed at predictingepigenic fracture developed zone. Curvature analysis is one method that predicts high permeability region of coal reservoir by use of coal bed structure curvature, combined with the fracture and cleat developed degree of outcrops. Synthetical evaluation according to prediction result of stress field and curvature will lead to high permeability region prediction of coal reservoir. It puts forward that the open degree of coal reservoir increases with the enhancement of major stress difference by means of the linkage of maxim major stress difference and coal bed physical quality. When major stress difference is larger than lOOMpa, permeability of coal reservoir is larger than 1 .0md. Stressing at looking for high permeability region, considering preservation condition, it evaluates synthetically four beneficial regions for CBM exploration and development, including the three best beneficial regions. Industrial CBM production in Jinshi No.1 well district and Tunliu district is the best verification of the research achievement.