XY fields in offshore East Kalimantan, Indonesia, have a history of whole drilling fluid losses ranging from continuous seepage to catasthropic losses in its “high amplitude carbonate body??. Even though these carbonates are well known and documented, have been closely predicted and well anticipated, and drilling program account for their occurrence, whole drilling fluid losses continued to plague drilling operations and result in highly cost of drilling fluid losses, require expensive treatments and incur Non-Productive Time (NPT)

Drilling programs call for controlling Equivalent Circulating Density (ECD), matching Rate of Penetration (ROP) to hole cleaning efficiency and reducing surge and swab pressures when loss zones are expected. Standard Lost Circulation Materials and Loss Prevention Materials (LCM and LPM) had been previously prepared and pumped prior to entering the loss zones with unpredictable and less than desirable results.

A special, Indonesia-sourced and manufactured, patented organic cellulose fiber was introduced in the fluid system to prevent losses prior to drilling the troublesome formation. A rapid, inexpensive, easily understood and applied, field test procedure have also been introduced for further development which allows a quick and accurate assessment of fluid system permeability sealing effectiveness and avoid over-treatment with fluid additives due to treating “on schedule?? or “by formulation??.

A significant improvement was shown for the first trial on X107 well and also on one exploration well. Success was achieved due to the ability of the Lost Prevention Material additives to create an effective wellbore seal in the troublesome formations. Drilling was continued without incurring NPT due to drilling fluid losses or remedial treatment requirements.

This paper presents and describes case histories which will detail material types and grades, function of the patented material, specific application and treatment details and compare time and cost savings to offset wells.

Introduction
Total E&P Indonesie discovered two offshore gas fields X and Y in 1986 and 1992 respectively. Located 30 km from the Tunu field, the size of X and Y field are approximately 58 km² for X field and 78 km² for Y field (Figure 1). They are located on shelf edge, near a shelf break. They have quite complex lithology with a complex structure in a depositional environment. In the upper part alternation of clay, sand, interbedded sandstone/claystone with lignite, organic shale and limestone streaks while the lower part consists of shale interbedded with thin to medium sandstone or calcareous sandstone with a chance of limestone streak.

Background – Losses Hazards
Highly fractured carbonates present in a depth range between 1,800 mTVD to 2,100 mTVD. Losses are prognosed to experience within carbonates layer named A2 and A3. These carbonates, highly fractured (up to 20 meters thick), have induced several. Non-Productive Time (NPT) during exploration and pre-drill campaign.The thickness of the layer determine the severityof the losses, from seepage to severe losses. There are two hypotheses about the nature of the formation which could be the origin of the drilling fluid losses:
1. Palaeokarst or carbonate dissolution
2. Fault related fracture

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