绒囊钻井液处理煤层气钻井上漏下塌地层的施工工艺

煤层气钻井经常钻遇上漏下塌地层,通常采用调换或调整钻井液来防塌控漏,但常常会因目的不一致而难以奏效。为此,针对不同层段漏失与坍塌控制主要需求,通过室内实验优化不同钻井液性能范围及指导配方,配制封堵性能由弱到强5种配方的绒囊钻井液封堵0.1 mm、1.0 mm、2.0 mm宽的裂缝,有针对性地形成了现场新浆配制、老浆维护等工艺,并在多个区域现场完成了超过5井次的绒囊钻井液工艺应用。实验评价结果表明:(1)以封堵相同宽度裂缝至驱压20 MPa的升压周期表征体系封堵性能强弱,优选出随钻控漏、随钻堵漏、静止堵漏3套钻井液配方;(2)以饱和煤柱塞后单轴抗拉强度、三轴抗压强度增幅表征防塌性能强弱,优化出坍塌风险分别为低、中、高煤层适用的钻井液配方;(3)根据钻井液消耗速度优化新浆补充速度,以排量、表观黏度降幅及实验得到提升表观黏度等指标确定优化老浆维护工艺所需的处理剂用量;(4)现场应用效果表明,钻井流体在对付漏失、坍塌地层前,调整好性能,是取得成功的关键。结论认为,通过调节绒囊流体不同的配方可以实现煤层气井内封堵控制漏失、坍塌,该工艺为煤层以及类似破碎性地层稳定井壁提供了技术支撑。

Application of fuzzy-ball drilling fluid technology to CBM gas wells through the strata with lost circulation in the upper parts and collapse in the lower parts

Complicated formations with lost circulation in the upper parts and collapse in the lower parts are often encountered during the drilling of coalbed methane (CBM) gas wells. And lost circulation and collapse are controlled generally by changing or adjusting drilling fluids, but with little effect due to the two different mechanisms. In this paper, laboratory tests were carried out to optimize the property range of different drilling fluids and instruct the formulas in order to satisfy the primary demand of different intervals, e.g. lost circulation and collapse control. Five formulas of fuzzy-ball drilling fluids, the plugging property of which is from weak to strong, were prepared to plug the fractures of 0.1 mm, 1.0 mm and 2.0 mm wide. Several technologies were developed specifically, e.g. on-site new fluid preparation and old fluid maintenance. The fuzzy-ball drilling fluid technology has been applied on site in many areas for more than 5 well times. And the following results were obtained on the basis of experimental evaluation. First, the pressure rising cycle from plugging the fracture of the same width to pressure rising to 20 MPa is used to characterize the plugging capacity of the fuzzy-ball drilling fluid system. Three drilling fluid formulas are selected and optimized, including lost circulation control while drilling, fracture plugging while drilling and fracture plugging while rig down. Second, the increasing amplitude of uniaxial tensile strength and triaxial compressive strength of the saturated core plunger is used to evaluate the anti-sloughing capacity. The drilling fluid formulas suitable for coal seams with collapse risk being low, medium and high are optimized respectively. Third, the supplying rate of this new fluid is optimized according to the consumption rate of drilling fluids. The dosage of the agent required to optimize the old fluid maintenance technique is determined according to the on-site pump rate, the decline amplitude of the apparent viscosity, and the experimentally measured apparent viscosity increase. Fourth, field application results show that the key to the success is to adjust the properties of drilling fluids well just before they are used in strata with lost circulation and collapse. In conclusion, lost circulation control and collapse prevention can be achieved by alternating the formulas of fuzzy-ball drilling fluid. This technology provides a technical support for realizing wellbore stability in coal beds and other similar friable formations.