Abstract

Drilling-induced formation damage is an area of concern when it comes to wellbore productivity, particularly for highly deviated / horizontal open hole completions. A great deal of effort has been devoted to understanding the damage mechanisms associated with Reservoir Drill-in Fluids (RDF), and to develop systems to specifically target bio-polymers and bridging agents in the RDF cake for improved wellbore clean-up. Experimental techniques to evaluate the performance of RDF clean-up treatments, however, have not received much attention. Due to its simplicity, the High Temperature High Pressure (HTHP) cell has been widely adopted by the Industry as a standard method to evaluate the performance of RDF filter cake stimulation treatments, but this technique has a number of limitations in terms of the quality and reproducibility of the deposited filter cake, as well as its ability to predict flow initiation pressure and return to flow percentage after the stimulation treatment.

This work compares the performance of two commercial RDF breakers in a GP application, under linear and radial flow conditions, using a HTHP cell and the Dynamic Displacement Radial Permeameter (DDRP) device described by Davidson et al. (2006). Unlike the HTHP cell, the DDRP cell can be arranged such that the RDF deposition, displacement, and stimulation stages of a horizontal Open Hole Gravel Pack (OHGP) can be simulated dynamically and sequentially, without system disruptions. The breakers evaluated are combinations of polymer-specific enzymes, chelating agents, and acid. Breaker "A" is a buffered acid system, while Breaker "B" contains a slow release acid precursor. The clean-up efficiency of each breaker, relative to a control system with no breaker, was determined as a function of flow rate using the DDRP device. These results were compared to those obtained under linear flow conditions with the HTHP cell. Significant differences were observed between the flow initiation pressure values measured with the HTHP cell and those measured with the DDRP, particularly for the system with no breaker. Differences were also observed in terms of percentage return to flow; higher percentages were consistently measured with the DDRP device. The difference between the percentage return to flow measured with the HTHP cell and the DDRP device was less than 5% for the system with no breaker, and 20% to 55% for the systems treated with the breaker solutions. In general, linear flow tests with the HTHP cell are useful as a pre-screening tool, but more sophisticated equipment such as the DDRP device can simulate downhole flow patterns and cake deposition more accurately and reproducibly. They also provide insight to important design parameters such as breaker activation time and flow rate dependencies of the clean-up treatment.

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