气侵条件下裂缝性地层漏失模拟实验

Simulation of the Lost Circulation in Fractured Formation under the Gas Invasion Conditions

顺北区块裂缝性储层发育,气侵和漏失复杂同存,严重制约了该地区的油气田开采。总结了顺北区块裂缝性储层气侵和漏失现状,并指出“先漏失后气侵”与“先气侵后漏失”两种漏溢同层模式。基于自制的钻井液动滤失与长裂缝封堵模拟实验装置,利用不同宽度楔形长裂缝模型,通过改变裂缝倾角、钻井液正压差和裂缝缝宽等不同裂缝性地层模拟情况,分析了气侵条件下裂缝性地层钻井液漏失规律。结果表明,垂直裂缝形成的封堵层最致密,气侵条件下承压能力较高,钻井液漏失深度为37.8 cm,但反向承压可达0.35 MPa,超出水平缝25%;钻井液正压差越大,漏失深度越大,3 MPa正压差漏失深度高达100 cm,比1 MPa条件下超出1倍;缝宽越大,漏失深度越大,形成的封堵层越多且致密,承压能力有一定提升,3 mm缝宽反向承压能力达1.12 MPa,超出1 mm缝宽65%,但气侵速度高达1.69 L/min。

The development of fractured reservoirs in the Shunbei Block,with complex coexistence of gas invasion and loss,has severely restricted the exploitation of oil and gas fields in the area.The current situation of gas invasion and loss in fractured reservoirs in the Shunbei Block was summarized,and two loss modes of gas invasion and loss in the same layer were pointed out including“loss first and then gas invasion”and“gas invasion first and then loss”.Based on a homemade drilling fluid dynamic loss and long fracture plugging simulation experiment device,wedge long fracture models with different widths were used to analyze the gas invasion of drilling fluid loss in fractured formations,by changing the fracture dip angle,positive pressure difference of drilling fluid,and fracture width,etc.The results show that the plugging layer formed by vertical fractures is the densest and has a high pressure bearing capacity under the gas invasion conditions.The drilling fluid loss depth is only 37.8 cm,and the reverse pressure can reach 0.35 MPa,which is 25%beyond the horizontal fracture.The larger the positive pressure difference of drilling fluid is,the greater the loss depth is.The loss depth of the positive pressure difference of 3 MPa is about 100 cm,which is more than double that under the condition of 1 MPa.The larger the slit width,the greater the leakage depth.The more and denser the plugging layer is formed,and the pressure bearing capacity is improved to a certain extent.The reverse pressure bearing capacity of 3 mm fracture width is 1.12 MPa,which exceeds 65%of the 1 mm fracture width,but the gas invasion speed is as high as 1.69 L/min.