Cased-Hole Pulsed Neutron Logging as alternative of Fluid Analysis Sampling Test in Mature Field Development

Abstract

To optimize the efficiency of operation in Mahakam as a mature field, the industry must improve the cost efficiency of maturing assets as compensation of the declining production and high fixed cost. one- phase-well (OPW) is one of the propose solution to tackle the producing hydrocarbon challenging in mature field, which is a well architecture without 9-5/8" surface casing. In OPW scheme, well is drilled in one section only using a diverter, no BOP, from surface to TD. For safety reason, the conventional pressure temperature fluid analysis (PT-FA) logging, as the ultimate method to determine the potential of reservoirs, can no longer be performed in OPW.

Indeed, PT-FA sampling log plays significant role in evaluation of fluid status identification. As alternative, a cased-hole Pulsed Neutron Logging (PNL) is then chosen to substitute PT-FA. It is challenging because in principal, those two logging completely have different objective and measurement. Before implemented in the next future OPW, comprehensive experiment has to carried out to convince that PT-FA logging can be displaced by PNL logging. PNL both conventional and advance, then were run in three recently drilled wells which have complete open-hole (OH) logs dataset along with fluid analysis (FA) and mudlog information.

PNL is the interaction between neutron and formation, which corresponding primarily to the amount of hydrogen in the formation. In Mahakam, PNL always encounter field limited conditions such as tight formation (shally-sand typical) and fresh formation water sand. A conventional PNL for gas detection require high formation water salinity, so it is almost impossible to achieve the optimal condition. Advance PNL measure fast neutron and less dependence to salinity and provide better detail fluid identification in tight formation.

This paper will discuss the risk and uncertainties of using a cased-hole PNL logging to replace PT-FA sampling data in specific condition encountered in Mahakam area.