Pressurized MudCap Drilling (PMCD), a variant of Managed Pressure Drilling (MPD), is known for allowing drilling to continue despite a total loss of circulation, while at the same time monitoring and controlling the entry of influx into the wellbore. A weakness of this technique is that the well still has to be killed prior to pulling out of the hole, which can be time-consuming and ultimately lead to reservoir damage. Utilizing a downhole isolation system to eliminate the need to kill the well during and after PMCD operations would therefore greatly improve the efficiency and effectiveness of this drilling technique and enhance its acceptability in operations where well productivity is a major consideration.
A combination of MPD and downhole isolation technologies was recently used successfully to drill a highly prolific, fractured gas reservoir in Suban Field, South Sumatra, Indonesia, resulting in wells capable of producing in excess of 300 mmscfd. MPD with downhole isolation allowed drilling to continue even with total loss of circulation, increased the safety margin of operations, reduced the amount of mud and lost circulation materials (LCM) required, minimized formation damage and made the running and installation of the completion assembly possible without the need to kill the well. The project demonstrated the clear and practical advantage that can be gained from combining these two technologies.
This paper focuses on how MPD and downhole isolation technologies were successfully integrated to produce high-rate gas wells in the Suban field and details how the system was effectively utilized for the first time to produce improvements in the safety and efficiency of drilling and completion operations, as compared to previous methods used in the area. It will also present the equipment, set-up, processes and procedures used in integrating these two technologies.
The Suban field is located in the ConocoPhillips Indonesia Corridor Block PSC of South Sumatra and has gas-in-place estimates in excess of 7 TCF. Suban Field was discovered in 1998 and with production starting in December 2002 from fractured basement rocks as well as overlying clastic and carbonate units. Table 1 shows the basic reservoir properties of this field, while Figure 1 provides its location.
ConocoPhillips currently operates the development of the field. Partners include Talisman and Pertamina. In 2004 ConocoPhillips recognized the opportunities of utilizing big bore wells for its Suban field development.
Early field production was dominated by two wells with extensive reservoir fracturing. Production potential from the reservoir was considered excellent and using well test data, it was determined that the fracturing system was well connected and that large areas of the reservoir could be drained from central locations.
While production rates were relatively high, it was clear that performance from these early completions was less than optimum and that the 5 ½" production tubing strings were under-sized relative to reservoir flow potential. Poor well flow efficiency was evidenced by large apparent non-Darcy skin effects seen from multi-point flow tests and pressure buildup tests. Non-Darcy skin is a term used to characterize a pressure drop near the wellbore that is caused by turbulent flow that increases as a function of the flow rate. In simple terms, it was apparent that well flow potentials could be much higher, if the non-Darcy effects could be eliminated or reduced.