A LESSON LEARNED OF FORMATION PRESSURE MEASUREMENT AT S-X1 and S-X2 WELLS, SUNGAI GELAM AREA, JAMBI

Abstract

Sungai Gelam Structure is one of the backbone structures in Jambi Field. Air Benakat Formation has been proven as the main productive formation. The challenges of reservoir in Sungai Gelam are reservoir characterization, unknown potential layer’s hydrocarbon bearing, and formation pressure issue.

The formation pressure measurement in this field was run in two wells, with operational problems occurred in each wells. The formation pressure data is very important for better understanding of reservoir’s pressure regime due to highly related fault system and to identify other potential layers. The initial operational problem occurred in S-X2 well, related to the probe on  instrument string which not set properly that resulted in lost seal, even when tested in casing. Fishing job was also been done due to cable stuck in run #2, and the further study shown that the differential pressure between formation and wellbore is too high, another highly probable reason was the trajectory of the well was skewed from the drilling program.

Air Benakat Formation (ABF) is commonly known for its poor rock properties (tight). In both S-X1 and S-X2 wells, formation  pressure measurement was defined within 15-20 stations, and a total of 61 attempts were conducted due to tight, supercharged and loss seal problems. The data gained shows that the main target has higher formation pressure than the prognosed; based on reservoir simulation, interpreted located in different block faulted and the unprognosed hydrocarbon bearing sand is shown from fluid analysis with virgin formation pressure.

This formation pressure has proven to measure formation pressure in tight sand, even failed in some sands, but the operational problem occurred lead us to consider another option of measurement method, ie measurement while drilling method to give a clearer reservoir characterization.