Shenquan Block Formation Esh Rheological Properties And Wellbore Stability Analysis

Specific technological study on the characteristics of complex formation and understanding of their mechanism and relevant rules are of great significance in developing corresponding engineering technology programs and avoiding related drilling risks as, with the continuing growth of the petroleum industry of China, more and more complex formations will be encountered during drilling.Rheological formation, as one of the typical complex formations, is extensively distributed in oil or gas fields of China such as Xinjiang, Sichuan, Zhongyuan and Jianghan. Field practice indicates that the problem of wellbore instability is relatively prominent when rheological formation is encountered during drilling due to the heterogeneity of stratigraphical sedimentation, which makes the drilling more difficult. Therefore, while studying the rheological properties of formation, if the analysis and study of wellbore stability are also taken into consideration, it will be conducive to proposing safer countermeasures solving the difficulties of drilling such complex formation so that the completion program can be optimized and the goal of increasing drilling success rate can be achieved. The combination of studies is very important to such a big oil consumption country as China, and its application prospect is extensive.This paper mainly carried out the following studies with Shenquan block as the main research target:1. The real-time drilling data of 14 wells in Shenquan block were collected and analyzed, from which it is indicated that Shanshan group (Esh) contains large volume of salt-gypsum that is prone to creeping and causes hole shrinkage; therefore, phenomenon such as drill pipe getting stuck are likely to occur during drilling. What’s more, because engineering parameters such as mud weight used for drilling are not appropriate, wellbore instability will be caused while creeping can not be effectively inhibited2. Mechanical properties of rock were studied as follows:acoustic parameters and kinetic parameters were determined from 10 cores of Shanshan group (Esh) formation in Shenquan block in accordance with the standards of International Society for Rock Mechanics; besides, uni-axial and tri-axial compressive strength tests were conducted, and rock mechanics parameters calculation model was created. Rock characteristic parameter profile was calculated and established using logging data.3. Formation pore pressure calculation model in Shenquan area was established; and the rules of horizontal and longitudinal distribution of formation pore pressure in this area were calculated and analyzed combining the logging data.4. Analysis was carried out against the salt-gypsum characteristics of Shanshan group in Shenquan block; constitutive equation was established based on clear understanding of the distribution rules of geostress. Simulation study was carried out on the rheological characteristics of salt-gypsum layer by means of the FLAC3D software; a model that can describe the rheological behaviors of salt-gypsum layer in this area was confirmed; the drilling fluid spectrum that inhibits flow stress of formation was calculated and drawn.5. Formation breakdown pressure calculation model was created through analyzing the force-bearing condition of the surrounding rocks in hole bottom based on Mohr-Coulomb Failure Criterion; formation breakdown pressure profile was calculated and drawn by combining the logging data; the scope of mud weight safe for maintaining wellbore stability is analyzed, and verification and analysis were carried out combining the drilling fluid spectrum that were established to inhibit the flow stress of formation; meanwhile, corresponding drilling fluid system against such characteristics as dissolution rate of cuttings was designed based on the supposed expansion inhibitive capability and saturation of drilling fluid for salt-gypsum layer. A set of drilling and completion techniques featuring safety and fastness suitable for Shanshan group (Esh) formation in Shenquan block was developed through analyzing and studying the rheological properties and wellbore stability of the Shanshan group (Esh) formation in Shenquan block. It meets the demand of safe production, reduces or avoids occurrence of complexities during drilling and completion in Shenquan area, increases rate of penetration, shortens drilling cycle, expands exploration achievements and meets the demand of exploration development.