Before Drilling Borehole Wall Mechanical Stability Study

In recent years, with the increasingly deepening depth of petroleum exploration and appearance of various advanced drilling technique, hole stability has attracted a lot of attention. So, the focus of research in a long run is flow to analyze the stability of undrilled layer to promise a fast and safe drilling and weaken the pollution to reservoir.Pointing to the problem of hole stability before drilling, this thesis establishes a stable wall mechanics models, adopting normal logging methods and analyzing the distribution of wall logging by means of mechanics. Regarding the density data and acoustic data in logging material as restriction, it also establishes undrilled district log through model seismic inverse, then, calculates elastic constant of rocks, density constant of rocks and even the profile of the following three pressures (pore pressure, caving pressure, fracture pressure). In the end, this thesis can determine safe drilling mud density windows, provide reference for drilling design, guides safe drilling and decreases the occurrence of accident. The contrastive analysis to the safe drilling mud density and the practice drilling mud density by the eight wells located in the Daniudi gas field indicate that this means is feasible and more accuracy, can met the needs of engineering executive.It is found that poisson ratio, tensile strength, horizontal stress contrast, cohensive force, angle of internal friction and formation pore pressure have effect on safe drilling mud density windows through analyzing the sensibility of formation parameter. So ,it is also essential to ascertain formation elastic constant and intensity constant in order to analyze hole stability.Since calculating pore pressure is of importance in establishing profiles of three pressure, this thesis adopts normal equivalent depth method and one-dimensional compaction theory to calculate pore pressure. The result shows that equivalent depth method has a good effect on the layer with abnormal pressure, which the one-dimensional compaction theory is more applicable. In calculating reservoir stress, this thesis chooses to calculate structural stress coefficient by broken leak experiment, and reservoir stress by combining calculating models of separate reservoir stress data of acoustic and density and provide continuous reservoir profiles for mechanics model to calculate safe mud density because of the high expense of in-house experiment, big error of reservoir stress by stress avalanche and the worse effect by hole-size elongation of non-stress.In the process of analyzing hole stability, the core and premise is inversion of seismic material limited by logging. Seismic inversion theory(mainly model seismic inversion), seismic wavelet assertion and data processing of seismic inversion are introduced in the following parts. The model inversion is processed according to two survey lines of two-dimensional seismic data in exploration area located in the central and southern part of Sichuan province. This thesis establishes acoustic logging data and density logging data, then figures out three pressure profiles of undrilled well and rock mechanics parameter of formation, gets safe drilling mud density windows and realizes the calculation of safe drilling mud density windows before drilling. It was improved by Wangjia No.1 practice drilling mud density that prediction safe drilling mud by use of seismic inversion is accuracy and in possession of engineering utility value.