Abstract

This paper examines the role of drill solids in causing formation and completion damage in horizontal openhole completions. Drill solids are routinely kept to a minimum in drilling fluids, mainly to improve drilling properties. However, these drill solids, even at low concentrations, represent a significant source of insoluble particulates that become incorporated in the drill-in fluid filtercake. Not only is the potential for formation damage greater, but these filtercakes laden with insoluble drill solids can be deposited on screens resulting in reduced productivity through screen plugging.

The objective of this paper is to illustrate the effect of drill solids contained in drill-in fluids on formation damage and well screen plugging and to emphasize the importance of minimizing solids, not only to maintain the desired drill fluid rheology, but also to effect better filtercake cleanup. New laboratory test methods have been used to study formation damage in a 2-foot long horizontal wellbore model incorporating dynamic filtercake deposition on natural and synthetic core material. The model measures formation damage in radial flow. Formation damage tests with drill solids were performed for both water based and synthetic based drill-in fluids. Testing was also performed to simulate prepacked screen damage using a variety of commercially available drill-in fluids and common resin-coated gravel sizes. Results of these tests with laboratory-prepared fluids have been compared against the performance of field fluids and will eventually be correlated with field well performance.

Background

The use of horizontal wells to maximize recovery of oil and gas has become commonplace. However, operators frequently find horizontal wells do not provide the expected productivity after completion. While cased hole completions exploit perforation techniques to bypass the zone of formation damage caused by drilling, the openhole completions commonly used in horizontal wells do not provide a means of bypassing this damage.

Previous work has discussed formation damage caused by drill-in fluids. Often, these studies have concluded that formation damage is caused by solids invasion into the rock or from damage caused by incompatible fluid filtrate. Some investigators have presented evidence that DIF filtercakes did not penetrate into rock matrices. Fraser's study showed ESEM photo images of different types of DIF filtercakes tightly compacted onto formation rock surfaces. He found very little filtercake invasion in the rock matrix. Burnham and Browne have discussed the concept of "lift off" pressure that can be used characterize the behavior of DIF filtercake on formation rock. Their studies suggest that "formation damage" can be caused by too "tight" a filtercake on rock surface.

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