Development And Performance Evaluation Of An Oil - Based Foam Drilling Fluid

When water-bearing formations are encountered in gas drilling, usually first convert to water-based foam drilling, but this process could easily lead to wall collapse. Using water-based foam could cause the hydration swelling of shale in water sensitive formation and reservoir damage. In this paper, on the basis of the investigation of a large number of literatures at home and abroad, a foaming agent is optimized and a new foam stabilizer is developed. Meanwhile, the foaming and stabilization mechanism of oil-based foam is analyzed. Then an oil-based foam drilling fluid is developed successfully and evaluated its performance. The concrete research contents and results as follows:(1) When conventional surfactants add to oil, the surface tension changes little, and even tends to rise. However, the diesel is commonly used as defoaming agent for water-based foam drilling fluid at the scene. In order to solve this problem, a foaming agent named ZSP is optimized consisted of organic silicon surfactants ZS and span20. ZSP has good foaming property and high tolerance to fight pollution and temperature.(2) A new foam stabilizer named SI is developed by monomer A and monomer B using emulsion polymerization, and then the polymerization reaction of experimental condition is optimized at the same time. The optimized conditions is monomer A28.0g, monomer B72.0g, emulsifier1.5g, molecular regulator0.5g, sodium phosphate0.3g, initiator0.6g and synthesis temperature50℃. The synthesized foam stabilizer is evaluated by using Waring-Blender method. Results show that it can significantly increase the foam stability foamed by different foaming agent in different oil.(3) The oil based foam stabilization mechanism is studied. Through the indoor experiment, the influence of oil-based foam stability caused by surface tension, foam viscosity and liquid viscosity is analyzed. Based on the experimental research, the main methods to stabilize the oil-based foam are got, namely to reduce the surface tension, increase foam viscosity, liquid viscosity and flexibility of surface film.(4) The optimum formulation of the oil-based foam drilling fluid (base fluid (diesel)+0.9%ZSP (0.54%ZS+0.36%Span20)+0.1%SI+0.3%DX) has been developed through screening oil-based foam agent, oil-based foam stabilizing agent and viscosity increaser. The synthetic performance of this foam drilling fluid has been evaluated. This foam drilling fluid has good foaming property and high tolerance to fight pollution and temperature. At the same time, the effect on oil-based foam to stabilize borehole wall is analyzed by rolling recovery and hardness test. The results show that oil-based foam has good inhibition performance to stabilize the borehole wall. The effect on oil-based foam to stabilize borehole wall mainly reflects in the strong inhibitory, sealing and leakage protection function, hydrophobic properties and capillary resistance, low density and reducing the soak time and contact area of formation water.