Abstract
Experience has shown that adding suitable particles to the drilling fluid can significantly improve the formation strength. This is especially beneficial when drilling wells with a narrow operational window as is typically the case when drilling depleted reservoirs. Successful operations have employed several types of particles, including graphite and calcium carbonate. For this kind of approach to work, it is important to establish an optimal particle composition in the drilling fluid. In a recent paper, SPE 107574, the possibility for continuous monitoring of the particle size distribution (PSD) and particle content in the drilling fluid, was demonstrated. This present work shows how these findings have allowed deploying a unique technique for running of solids control equipment in a North Sea offshore field, providing optimal particle concentration and size distribution when drilling a significantly depleted reservoir. We describe in detail an HTHP offshore operation where coarse shaker screens were used to allow relatively large particles to re-enter the well during circulation. These particles act just like particles deliberately added to the drilling fluid in order to enhance formation strength. The monitoring equipment allowed for close control of the PSD of the drilling fluid flowing into and out of the well during drilling. The particle size distribution is compared to that obtained with conventional additives previously used to achieve formation strength enhancement.
