Abstract

This paper describes the application of a nondamaging temporary gel system to isolate a part of a horizontal section in an openhole well. The purpose of this application was to provide a cost effective method of isolating a high water-saturated zone of the extended lateral to facilitate the production of hydrocarbon from the rest of the open hole.

The candidate well (R-91) selected for this application was the first extended lateral horizontal well (3000-ft lateral section) drilled as a producer. The well was to be converted to an injector at a later time.

Logging while drilling (LWD) was performed during the drilling phase of this well, and a low-resistivity section was identified along the horizontal lateral. On completion of the drilling, a well test was performed, indicating a high water cut. It was suspected that this water was being produced from this low resistivity section along the lateral hole.

An economical method for confirming and isolating the source of this water influx was needed. Since this was a low-pressure well, an electric submersible pump (ESP) for production had been used. Since low-pressure wells were the norm for this field, ESP completions were commonplace. Different techniques, including use of drillpipe conveyed or coiled-tubing-conveyed production logging tool (PLT) were also considered.

The nondamaging gel plug placed across the low resistivity section of open hole with coiled-tubing allowed the operator to identify and confirm the source of water. The gel plug formed a barrier across this zone, thereby restricting and reducing the water influx.

Presence of a natural fracture was also identified during the drilling phase, and hence, communication between the low-resistivity interval with the oil zone towards the heel of the lateral section was confirmed. Due to non-availability of certain logging tools at the time of requirement along with high costs of using such tools, the proposed gel technique was used as an alternative option. Being a non-damaging pill with greater than 99% regained permeability after cleanup, the well could safely be isolated with this technique. The pill would be dissolved with acid at a later stage when required.

The procedures and the placement techniques of using two-inch coiled tubing and subsequent test results provided insight into the success and the uncertainties involved.

The post-job analysis of results allowed further optimization of these processes, which would facilitate similar applications in the future.

The operator's objective of drilling this well to initially produce as much oil as possible, and then, at a later stage to convert it into an injector to improve the sweep efficiency in the area was achieved as a result of the application of this technique.

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