Calculation Of Rock Mechanics Parameters Of No.11 Coal And Its Roof And Floor In Hancheng Block And Prediction Of Favorable Development Zones Of Coalbed Methane

Hancheng Coalbed Methane(CBM)development zone locates in the northeast of Weibel uplift in Ordos Basin,one of the main CBM development zones in China.Through the systematic collection of previous research results on the research area,combined with the characteristics of block data,this study uses conventional logging array,sonic logging;micro-resistivity image logging;core analysis data;fracturing data;monitoring results and other data to investigate the fine in-situ stress calculation model of No.11 coal in Taiyuan formation.This paper makes full use of the basic theory of fine in-situ stress and the successful oil and gas experience as the guide,discusses the main control factors of coal seam gas"enrichment and high seepage.And it establishes the relationship between the content of microscopic coal macerals and logging response.It reveals that the radioactive'Th'element is abnormally capable of indicating the'sweet spot area'of CBM.Moreover,it predicts the favorable area for No.11coal of Taiwan formation in the research area.The research has reported:(1)The current maximum principal stress in the study area is 45degrees in the northeast direction.(2)The characteristics of in-situ stress distribution:with the increase of buried depth,the horizontal stress difference gradually becomes larger.The overall horizontal stress of the top and base plate is lower than that of the coal seam;?hmax??v??hmin.(3)The sensitive logging parameters of coal vitrinite content are natural gamma-ray value,deep-shallow resistivity ratio,neutron porosity,and other parameters.The vitrinite content is directly proportional to neutron porosity,but it is inversely proportional to natural gamma and deep-shallow resistivity ratio.(4)The positive anomaly of the radioactive'Th'element can better indicate the'sweet spot area'of the CBM,perhaps because the radioactive elements reduce the hydrocarbon threshold of hydrocarbon source rock.While other coal seams have just reached the hydrocarbon threshold to produce methane,these abnormal reflective sections of the coal seam have produced a large amount of methane.Methane production makes the coal seam cleat under effective stress reduction;many cleats can thus be retained.(5)The preservation of CBM is mainly damaged by fracture and hydrodynamic conditions.By predicting the middle of the North Xuefeng well field,the South Xuefeng fault zone,the West and East of Banqiao well area,these areas are far from disturbances of fractures and shallow hydrodynamic fields,the content of CBM is above 8m~3/t.Large faults are developed in these regions(the middle of Xuefeng and Banqiao well area,the nose-like structure in the east of Xuefeng well area),and some are close to the near-surface fault system.A large amount of CBM has suffered effusions.Therefore,the content of CBM in these regions is predicted to be between1 and 4m~3/t.(6)The coal cleat permeability is mainly affected by the situation about face cleat development and open.The ratio of deep-shallow resistivity responds obviously to coal seam cleat logging and can quantify the degree of cut development.Under the action of the current stress field,the eastern face cleat orientation of the study area is close to 90 degrees,with the maximum main stress angle at the present level.When the surface cleat is closed state,the maximum level of the western cleat of the study area reaches nearly 45;the face cleat is relatively open.Also,the"X"shears associated with small low-dip inverse faults improve the permeability of the partial coal seam.It is predicted that cleats are well developed in the middle part of the Xuefeng well area and nose uplift but sporadically developed in the middle part of the Banqiao well area.(7)Coal seam thickness,gas content,and permeability are the main control factors to control the high yield of CBM enrichment,according to the optimized thinking of the favorable area of"enrichment and high seepage."The first step is to superimpose and analyze the thickness and gas content of the coal seam,determining that the thickness limit of the coal seam in the enrichment area is 3m,and the gas content limit is 4m3/t.The enrichment area is divided into two kinds of enrichment areas.The second step is to superimpose the enrichment area with the high seepage area of the coal seam.The actual CBM recovery is a limiting scale for calibrating permeability,then determining the lower limit of the effective penetration rate of the second favorable area is 0.05m D.The lower limit of the first favorable area is 0.1m D.By dividing the favorable areas into four categories,the results show that the first favorable area of No.11 CBM development only distributes in the middle of the Xuefeng area.The second favorable area distributes in the middle and west of the Xuefeng district.The third favorable area mainly locates in Xuefeng well area.The fourth favorable areas are in the Xuefeng well area and the northern part of the Banqiao well area.The other areas are not conducive to exploit the No.11 coal seam.