An Integrated Pore-Pressure Prediction Approach: A Success Strategy to Develop Deep Gas Reservoirs by Drilling through a Highly Depleted Shallow Zone, Semberah Field, East Kalimantan, Indonesia

摘要

The Semberah field is one of the main oil and gas producing areas operated by VICO Indonesia in East Kalimantan, Indonesia. Production from this field has been focused mostly from shallow-level reservoir (C-I intervals). After production of more than 30 years, the shallow and high-permeability intervals are currently highly depleted. Meanwhile, deep and low-permeability reservoirs (J level) have rarely been penetrated leaving significant reserves. Accessing these reserves is a highly challenging work today. A recent well was drilled to access the reserves in a J sand but the drilling had to be stopped earlier due to total loss of circulation whilst penetrating a shallow high-permeability and highly depleted sandstone I082A. An integrated pore pressure prediction approach has been carried out during the planning of drilling and completion of a proposed S86 well. The objective was to successfully access deep target reserves in the J sandstone by safely drilling through the highly-depleted I082A sandstone. The approach integrated available data including well logs, cores, formation pressure, historical-match derived pressures, and drilling parameters. Pore pressure prediction showed that the proposed S86 well would penetrate normal pressure regime (8.45 ppg) to -8,500’ SS. Within this interval, variously depleted reservoirs (3-6 ppg) would be penetrated. Starting from -8,500’ SS to -10,680’ (TD), the well was predicted to enter overpressure environment (8.45-13 ppg). Within the environment, a higly depleted I082A with 500 psi (0.87 ppg) was estimated to be encountered at ~8,819’ SS. The pore pressure prediction study recommended 1) to drill with normal mudweight of 10-12 ppg and set 9-5/8” casing point before penetrating I082A sandstone, 2) to drill through I082A to its bottom with low mudweight (8-9 ppg) and isolate with 7” short liner, 3) drill 6” open-hole to TD with high mudweight (12-13 ppg). The newly proposed well safely drilled through the highly depleted I082A sandstone and access to the reserves in the targeted J sandstone was successfully achieved. This great success has opened up an opportunity for further development drilling in the Semberah field.