The wells in Soka field in onshore South Sumatra, Indonesia are drilled through a fractured carbonate reservoir (Baturaja formation) where severe circulation losses and kicks while drilling are commonplace. Drilling in one of the wells in the field, Soka 2006–1 was suspended for two years due to total losses combined with gas kicks. Almost two months were spent after total loss of circulation was experienced trying to control and drill Soka 2006–1 to no avail. The well was plugged and abandoned on July 2006 with the intention of returning to it and finishing it once an appropriate approach can be developed to address the drilling issues that were encountered. The approach chosen for re-entry operations in Soka 2006–1 was a managed pressure drilling (MPD) technique called Pressurized Mud Cap Drilling (PMCD). A rotating control device (RCD) is the main component used in PMCD operations, the objective of which is to eliminate the non-productive time (NPT) associated with drilling when loss - kick scenarios occur. A new well, Soka 2006–6, was also planned to be drilled in the area using the same technique, but with the addition of a downhole isolation valve that was to be installed and cemented together with the last casing string above the section where losses are expected. The casing valve allows for safer and faster tripping operations and more importantly, can serve as a downhole lubricator that will help facilitate the running of the completion assembly in PMCD mode. A casing valve could not be installed in Soka 2006–1 as the casing string above the loss zone was already in place. This paper describes the planning and implementation of the PMCD technique in both the Soka 2006–1 and 2006–6 wells and discusses the results of the drilling operations. Furthermore, it explains how drilling in PMCD mode allowed re-entry operations in Soka 2006–1 to reach the target depth in less than a day after total loss of circulation was again experienced, and how the completion assembly was run and cemented in PMCD mode. Introduction The Soka Field is located on the Musi Platform of the South Sumatra Basin. Figure 1 shows the stratigraphy of the South Sumatera Basin. One of the wells to be drilled in the Soka field is Soka 2006–6. This well is proposed to reach the oil column at the Baturaja formation, and its main objective is the carbonate reef facies of the said formation. The well is designed to penetrate 681 feet of Baturaja limestone. Re-entry operations on another well, Soka D7 or 2006–1, is also planned to penetrate the Baturaja limestone by 371 feet, 95 feet of which consists of the oil column. Re-entry of Soka 2006–1 is intended to complete drilling operations on the well, which have been suspended for two years due to total circulation losses and accompanying gas kicks encountered while drilling in the upper section of the Baturaja Formation. Around one and a half months were spent after total loss of circulation was experienced trying to control and drill the original Soka 2006–1 well to no avail. It was plugged and abandoned on July 2006 with the intention of returning to it and finishing it once an appropriate approach was developed to address the drilling issues that were encountered. The utilization of the current Soka 2006–1 borehole for re-entry is intended to minimize drilling cost, since risk for drilling in Baturaja formation in this cluster is similar for other trajectories.

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The challenge to maintain production in marginal field and to keep any related activities to be economically justified will require more optimization and innovation. Artificial lift fields using pump require many mechanical well service intervention: to install and to repair the downhole pump. Mechanical well service uses well service rig or pulling unit rig, mainly to pull and to run the tubing. One of main component of the rig is well control equipment system. The complete package of the well control equipment system is about 30% of the rig service package. The equipment may consist of: complete BOP stack, hydraulic power unit with line, choke manifold, kill line and flare line, poor boy separator. The time needed to rig up, test, and rig down the well control equipment package has significant percentage. For simple job of artificial lift mechanical well service which main job is only pulling and running back the tubing, the percentage may be about 20% - 30%. Continuous and routine job of the mechanical well service will give significant cost impact to the total operation expenses. One of the marginal on shore fields in Tunisia, with low productive oil production well, requires innovation to keep the production in economic limit. Cost reduction of the artificial lift well service operation is one of the main options. Optimization of the well control equipment was studied to reduce the field operation cost. Careful risk assessment had been done. Simple and low cost well control equipment was prepared. Additional procedure was introducedandsome documents related to risk control are prepared. Applying the approach, about 25% - 30% of cost saving is identified without sacrify the safety of the operation. Well control equipment standard is an almost matured and well-regulated standard around the world. The main equipment standards are almost the same across regions, countries and companies. Mostly there are two categories of the standards related to well operation: drilling and well service. However, mostly the main well control equipment is the same for both drilling and well service. Off shore well control standard are more stringent than on shore operation. However, mechanical well service,which deals with existing perforation without any reservoir stimulation and very well-known production behaviors, are not specifically categorized in most of the standards. This type of on shore mechanical well service operation has much less risk than drilling or reservoir well service, so it is highly possible to use less well control equipment package with the proper risk assessment according to the field/well condition. The well control equipment applied in the Tunisia field will hopefully give more standard guidance for low risk marginal oil field.

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