Evaluation and Improvement of the Performance of Oil Base Drilling Fluids for Shale Gas Drilling
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摘要: 油基钻井液已成为开发页岩气水平井的关键技术之一,具有稳定井壁和保持井眼清洁的功能。通过评价中石油川渝地区油基钻井液体系的流变性、封堵性、固相含量和稳定性等性能,并结合这些井的井下复杂情况原因分析,得出封堵性是保持井壁稳定的关键,提高钻井液φ6值和排量可以改善井眼清洁,有害低密度固相含量的增加是导致钻井液性能恶化的主要原因。针对井壁失稳、井眼清洁和性能维护等问题,建立了纳-微米封堵评价方法,确定了有害低密度固相含量计算方法,并形成了页岩气油基钻井液技术规范,有望为页岩气水平井的开发提供技术支持。Abstract: As one of the key technologies in drilling horizontal shale gas wells, oil base drilling fluids are used to maintain the stability of borehole wall and to clean the hole. In this paper the rheology, plugging capacity, solids content and property stability etc. of the oil base drilling fluids used in PetroChina's Chuanyu development area are evaluated. From the evaluation and analyses of downhole troubles encountered in Chuanyu area it is concluded that plugging capacity of an oil base drilling fluid is the key in maintaining the stability of borehole wall. By increasing the φ6 reading and flow rate of the drilling fluids, hole cleaning can be improved. Deterioration of the performance of a drilling fluid comes mainly from the increase of low-density solids content in the drilling fluid. To resolve problems encountered in maintaining borehole wall instability, hole cleaning and mud property maintenance, a method has been established to evaluate the plugging capacity of nanometer and micrometer particles. A method of calculating the content of harmful low-density solids in a drilling fluid is determined, and a set of technical norms for maintaining the properties of oil base drilling fluids for shale gas development is formed, hopefully will provide a technical support to shale gas development with horizontal drilling.
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