Integrating Pulsed-Neutron Interpretation with Reservoir Drive Mechanism in Complex Completion Environment Towards Further Informative Development Plan: A Case Study from Offshore Asia

Abstract

Pulsed-neutron logging (PNL) interpretation in complex completion wells that aligned with reservoir drive mechanism expectation can be used for further development plan infill well with more confident. Robust workflow is required to adjust the parameter to be align with expected reservoir drive mechanism in dry gas field and edge water drives mechanism. With result from multiple wells, infill well decision for extending field life can be planned confidently.

Interpretation from both inelastic gas mode and sigma modes was performed in multiple wells by comparing result with and without having integrated reservoir knowledge using MCNP model in various completion scenario in the same well (gravel pack, casing only, tubing and casing with various fluid condition). Due to sensitivity of gas mode in this reservoir and wellbore condition, interpretation relies heavily on gas mode. Workflow parameters were adjusted to deal with shaly condition of the reservoir and to be aligned with reservoir mechanism knowledge such as dry gas reservoir gas expansion during depletion or edge water drive reservoir.

Saturation monitoring results from PNL tool reveals dry gas expansion mechanism which gas saturation remains comparable to initial reservoir except one particular direction with significant reduction in water saturation that suggests edge water drive mechanism. This result was based on PNL interpretation from multiple wells in the same field. Robust interpretation workflow from multiple MCNP were used to deal with various completion and fluid condition in tubing and annulus. The saturation result is sensitive to depletion in which accurate knowledge of current reservoir pressure minimize the saturation uncertainty and approach the initial reservoir saturation. Another important factor is Vshale correction in the workflow to deal with shaly sand reservoir that affect the final saturation result. The saturation result was calibrated with current producing section in which remaining gas saturation is still observed. Furthermore, the saturation result is also aligned in the existing perforation with fully water loading. With the result align to both expected reservoir drive mechanism and current production result, the interpretation then can be used as a basis for decision of infill drilling for extending field life.

Multiple wells PNL interpretation for saturation monitoring result that aligned with reservoir drive mechanism and current production results increase the confident in current reservoir fluid condition which leads to more information decision for future infill drilling decision. A collaborative effort between services company and asset teams led to more confident interpretation for future critical field life extension decision of infill drilling in the mature gas field.