Rupture-Resistant Filter Cake for Wellbore Strengthening

滤失通常发生在钻井过程中产生的裂缝中。为了避免这种现象，已经开发了一系列技术来提高井筒的完整性，阻止井漏，并允许在井筒压力超过裂缝梯度的情况下钻井。这些技术被称为钻孔强化。井眼强化机理的一个典型例子是在钻井液中加入分级物。当骨折发生时，这些分词进入裂缝，阻碍形成一座桥。然而，最近几年出现了一种新的井眼加固理论机制，即形成滤饼，由于渗透性地层中孔隙中的流体压力低于井眼压力，滤饼形成在井壁上。这项研究将包括室内实验和数值分析相结合的方法，以防止岩石地层中的裂缝及其扩展。将进行参数研究，以获得特定的滤饼特性(如渗透率、厚度和强度)，从而增加岩层中的裂缝梯度，从而将钻井过程中的流体损失降至最低。

Fluid losses usually occur through fractures caused by the drilling pro- cess. To avoid this phenomenon,a series of techniques has been developed to raise the integrity of the wellbore, stopping lost circulationand allow drilling with wellbore pressures in excess of the fracture gradient. These techniques are calledwellbore strengthening. A typical example of wellbore strengthening mechanism consists of addingparticiples to the drilling mud. When a fracture occurs these participles enter in the fractures and obstructit forming a bridge. However, in the last years a new theoretical wellbore strengthening mechanism hasbeen individuated which consists in the formation of a filter cake, which builds up on the wellbore wallsbecause the fluid pressure in the pore space in a permeable formation is lower than the boreholepressure.This research will involve a combination of laboratory experiments and numerical analysis of the efficiencyof the filter cake in prevent fractures in the rock formation and their propagation. A parametric study willbe con- ducted to achieve specific filter cake properties (e.g. permeability, thickness and strength), whichincreases the fracture gradient in the rock formation and consequently minimizes the fluid lossesduring the drilling process.