Research On The Theory Of Membrane Drilling Fluid And Its Applied Technology

Membrane drilling fluid with the property of semi-permeable membrane can form a layer of isolating membrane on the sidewall face, which performs as a kind of protective layer in the outer area of the sidewall to prevent the drilling fluid from filtrating into the formation. In this way, the membrane drilling fluid can effectively avoid the formation hydration expansion, borehole wall sloughing and seal off the formation fracture, which can finally protect the reservoir.In this paper, properties of semipermeable membrane and possibility of membrane forming were studied both based on membrane technology and physicochemical properties of shale. Membrane efficiency was calculated according to the equilibrium principle of chemical potential. After that, influence factors related to membrane efficiency of shale such as activity, ionic types, CEC, porosity and permeability were analysed qualitatively and quantificationally. Finally, an approach of improving membrane efficiency of shale was concluded. This paper established a method of reservoir evaluation which mainly contains physicochemical properties of shale and petrofabric. With X-ray diffraction analysis, thin-section analysis, SEM and CST testing, physicochemical properties of Yitong area in Jilin Oilfield were carefully researched, and the relation between degree of orientation and shale content was analyzed. The factors that lead to wellbore unstable in this area were found. A lot of lab experiments were conducted to illustrate the properties of core in Yitong area, such as:Core soak experiment, CEC testing, Zeta potential test, swelling test, cuttings roller recovery test and formation water activity degree test, of which results showed that the most evaluating indicators are at a small to medium degree, therefore the dilatability and dispersity of shale in Yitong area is medium.A series of drilling fluid tests have been made according to standard test program. A drilling fluid evaluation system including some evaluating indicators was formed, of which the membrane efficiency is primary, wellbore stability and reservoir protection is as a supplement. The synthetic evaluation indicates that membrane efficiency is up to 82%, which idealizes shale membrane. Furthermore, this drilling fluid system restrains clay hydration effectively, it has a high salt resistance and strong anti-contamination ability, reachs a high temperature resistance of 180℃and its properties is easy to adjust as well. Some test wells in Jilin Oilfield were directed by membrane drilling fluid. It made the drilling succeed, kept the borehole gauge regular and consistent, stabilized wellbore, and protected the reservoir efficiently.