Cased Hole Reservoir Evaluation as a Mean of Risk Reduction, Production Enhancement and Cost Control for Mature Fields: A Case Study from México's Northern Region

Abstract

As new reservoirs become more difficult and expensive to find and produce, the need to provide innovative solutions for mature fields and bypassed reserves has increased exponentially. México's North region's reemergence as an important focus of workover and development wells activity on a tight budget represents an interesting challenge for operators and service companies alike.

This review of three case studies shows how cased hole reservoir evaluation can be the key for solving different unfavorable scenarios that arise constantly in the fields in this area by applying the right mixture of technology and analysis.

The first case study is a gas well in the Burgos basin where the most productive reservoirs are reached after drilling though some formations known to cause wellbore instability including lost circulation and stuck pipe, often leading to sidetracking and even lost wells. All these factors used to make Open Hole logging a necessary risk that companies had to take. By applying a combination of through casing logging, gamma ray, neutron, density, sonic and a pulsed neutron tool that allows gas identification in very low porosity sands, a complete petrophysical evaluation was achieved avoiding potential stuck tools, fishing and hole abandonment issues thus lowering non-productive times. The main cost saver was rigless operations.

The second case study is a heavy oil well in the limestone reservoirs of the Tampico-Misantla basin, showing that this approach can be used across a wide range of wellbore and reservoir conditions.

The third case study is an old well located in a field that was subjected to massive and uncontrolled water injection for several years. Original Open hole logs painted a very optimistic picture of fluid saturation that proved inaccurate when the first wells from the intervention campaign started producing mostly injection water. Cased hole reservoir evaluation using advanced pulsed neutron measurement methods resulted in a total game changer for the wells near the injection arrays, providing a way to identify which parts of the reservoir were flooded by the EOR methods, which were depleted, and which represented bypassed reserves for production. This kind of workover campaigns cannot be overlooked since they represent the bulk of activity for mature fields trying to re-energize stalled projects by finding new opportunities for production.

These three case studies demonstrate the valuable contribution of cased hole reservoir evaluation and the importance it will have moving forward in this area of México and in general for mature fields worldwide.