Carbonate Stratigraphic Borehole Stability Log Evaluation Method

With the increasing of explorative difficulty in oil and gas field, the application of logging technology in petroleum engineering has been becoming more and more significant. Especially in wellface stability evaluation problem. The losing stability formation of carbonate profile mainly concentrate in these formations, in which stress lost balance, salt rock with creep deformation property, and fissure formation along with hard-fragile limestone formation. This dissertation is aimed at the drilling engineering accidents, such as the well spout, well leak, well collapse and wedging of drill tool during the drill well process in the triassic formation in north-east of Sichuan. The research work of the calculating model of rock mechanics parameters using loggmg datum, the logging prediction model of the stress and three formation pressure, and determining the secure window of mud density and the borehole wall losing stability mechanism and the precaution making full use of the merit of continuity, economical efficiency, reliability and high resolution of logging information.The dissertation begin with analyzing the force situation of the wellface surrounding rock, the method of calculating Poisson ratio are presented using logging datum by researching the model of calculating rock mechanics parameters model, when shear wave time is lacked. Meanwhile the method of calculating stress size and orientation are researched using conventional logging datum and image logging datum.Aiming at the problem which estimating formation pore pressure is relatively difficult, the effectiveness stress method is used to predict the formation pore pressure of the carbonate. Result show that the method has higher accuracy for calculating formation pore pressure of the carbonate. Based on analyzing comparatively some kinds in common use shear damage norm, the Mohr-Coulomb norm is optimized. The effects that the rock tensile strength is in pore formation and the fracture formation are sufficiently considered, the formation fracture pressure is established. The effects, which are the layer dip and the well deviation act as to three formation pressure, are researched, the secure window of drilling well mud density fitted for researching region are given. Based on three-constructed formation pressure of the carbonate logging calculation models, the secure window of mud density is given to guard against well collapse for the carbonate formation of research region.The common types of the carbonate borehole wall losing stabilization are briefly presented. The collapse mechanisms and reasons are researched according to types. On the basis of a variety of elements aroused the borehole losing stabilization in the actual drilling process, the countermeasures are proposed to guard against these complex accidents. Meanwhile, the predicting method of stress is proposed based on BP's neural network by using the seismic interval velocity, in order to predict borehole wall stability.Based on the above methodological model study, and combined the practical situation of FeiXianGuan series formation in the LuoJiazhai and ZiShuiba structure on the east-north of Sichuan, a set of borehole stability valuation application program fitted on carbonate is developed. Furthermore, the application program are used to Lj9 well and Zi2 well etc., the calculated stress, three formation pressure and the secure window of drilling well mud density are obtained to examine practice production, it can be meet to the necessaries of the actual drilling project of field.