Managed Pressure Drilling Overcomes Drilling Challenges and Enhances Oil Production of Naturally Fractured Carbonate Reservoir of East Siberia

Abstract

One of the main problems associated with drilling of the horizontal wells of high length under conditions of a low-porous carbonate fractured reservoir is catastrophic mud losses associated with zones of intense fracturing and cavernousness. The meeting of such zones leads to the risk of failure to achieve the project well length, which further negatively affects the reserves development. This article describes the technological, production, economic aspects of the introduction of managed pressure drilling (MPD). Managed Pressure Drilling (MPD) is an adaptive drilling process used to precise control the annular pressure profile throughout the wellbore. While conventional drilling uses the hydrostatic pressure of the drilling mud to manage pressure in the well, MPD uses a combination of surface pressure, hydrostatic pressure of the mud and annular friction to balance the exposed formation pressure. Control of these parameters allows maintaining the pressure at the bottom of the well close to the reservoir pressure, thereby avoiding mud losses or inflow of formation fluid into the well. Conventional drilling of highly fractured zone is accompanied with intensive mud losses. Over 50% of the drilled wells in the oilfield could not reach the final target. Average productivity index for short wells is 30% less than for those that reached planned horizontal length. Application of bridging agents and hi-vis pills partially allows to solve the problem, but negatively affects the productivity and cost of wells. As part of pilot stage, managed pressure drilling was tested on the two well clusters. 5 wells out of 7 reached the project length. The increase in the starting oil rate was 30%. The loss of drilling mud has significantly decreased. The average mechanical rate of penetration increased by 7%. Despite the high cost of the MPD, the ability to control the well during drilling reduces the final cost of the well by minimizing the loss of oil required to prepare the drilling fluid. According to the analyzed wells, the average cost of a meter of penetration for MPD is 14% higher than with standard overbalance drilling. At the same time, the unit cost of drilling per one ton of oil flow rate decreased by 22%, which indicates the economic feasibility of the technology. The paper presents a comprehensive analysis of the MPD, with an assessment of the impact on drilling performance (rate of penetration, mud loses), production characteristics of wells (starting production rate, productivity index) and economic effect (cost of 1m penetration).