The Research Of Fracture-cave Characteristics And Fracture Prediction Of The Pre-tertiary In Jizhong Depression

With the rapid development of economy, the energy demand is increasing in the world.Due to the research of new energy is blocked, the world does not get rid of the dependence ontraditional energy especially the oil and gas resources, oil resource has risen to the height of amatter of national security. It is found by exploration that the most high-yield oil and gaswells in buried hill reservoir are distributed along the fault-crack zone or karst pores band,while the development status of fault and fracture are closely related with the stress conditionof the region. Therefore, the research on crustal stress field and fracture plays an importantrole in oilfield exploitation. This paper is based on the previous research of ground stress androck cracks, taking the north region of Renqiu buried hill Ordovician in Jizhong region as anexample. The crustal stress of the researched region was simulated by using ANSYS, basedon local geology and logging data. The crack development in the region was calculated andthe influence of karst cave on stress distribution was studied. According to the research,thefollowing results can be obtained:(1) The rocks in this region are mainly brittle carbonaterocks. Structural fracture is the major crack type with some corroded fissures, while othercrack types are minor.(2) The rock mechanics parameters were obtained by logging data,which is a more economical and convenient way to define mechanics parameters and theaccuracy can be guaranteed. It can be used in the areas that are rich in well logging data.(3)The boundary conditions of this region are inversed by the method of solving staticallyindeterminate equation based on the least squares. It can be deduce that the boundarycondition acquired by forward modeling is closed to actual state by comparing simulated withactual values.(4) The principal stress in this region distributed generally in the50MPa-200MPa, except the areas that are larger affected by the boundary force loaded around. The northeast has a maximum value, that is greater than200MPa, and the southern fault has aminimum value, that is less than60MPa.(5) The effect of two caves with the profile arecircular and semi-circular on the stress distribution was studied. It is found that the stressvalues are greater around the circular cave and the cracks are easy to be produced whicnforming the migration pathways, while the stress value are generally low around thesemi-circular cave and it is difficult to form a through pathway.(6) The development situationof fracture is obtained through the combination of the calculated stress values with the rockfailure criterion. Compared with the distribution figure of the wells, it is found that the areasthat have intensive oil wells coincide with the areas which the fracture development indexsare high, which proves that the simulation is reliable.