Abstract

Optimizing the design of injection processes in sand control (i.e., conventional gravel pack and frac-pack) and stimulated completions as well as in injection wells has been a primary goal in selecting methods to improve cost and operational efficiency. It is well accepted that perforating with shaped- charge jet explosives has had a large impact on the efficiency of oil and gas completions in cased wells. However, accurate predicting of the impact of different perforating systems or operations can be difficult, as there are many variables in the process that can not be easily quantified; therefore, modeling the detailed physics of the process is complex.

This paper examines perforating as it relates to injection wells and/or injection processes. Experiments using field shaped-charge explosives were conducted under a variety of conditions with different cores to quantify injectivity compared to productivity. Results from the laboratory experiments were then compared to field data for validation. New knowledge and insights are gained to better understand and to optimize the design of injection processes in sand control completions and completion processes in injection wells.

Introduction

The impact of perforating systems (i.e., both hardware and operating conditions) on well performance has been well researched and documented1–3. Theoretical models,4–6 experimental data,7–8 and field studies9–10 have sought to optimize well productivity or injectivity by quantifying the relationships between well inflow performance and key perforating/reservoir parameters. However, there are relatively very few studies that focus specifically on injection, with most of these focused on field-specific injection problems.11–13

The limited focus on injectivity wrongly implies that it is identical to productivity and/or not of value. Water injection is critical to maintain reservoir pressure, and optimized well performance is valuable because there are relatively fewer wells dedicated to this task. Furthermore, injection processes are prevalent in completions requiring acid and fracture stimulation and sand control.

Most studies on injection damage focus on the importance of quantifying the injection fluid and rock interactions.14 Halleck et al.15 conducted an experimental study of perforating mechanical damage, measuring the rock hardness of the zone damaged by a 6.5 gm explosive shaped charge in three different cores. Blok et al.16, Wong et al.17 and Welling18 conducted experimental and field studies that related perforating and sand control completion damage. These studies confirm that there is much need for the integrated design of the perforation and completion systems to deliver optimized well performance in cased wells.

This paper details a perforation study that was performed to understand the damage mechanisms associated with injection wells and/or injection processes. In particular, it looks at how perforating charges and practices affect the capability to inject fluids based on several series of API RP19B19 Section IV flow tests performed in Berea and Castlegate sandstones.

The experimental study simulated a range of gun and shot conditions from perforating underbalanced using tubing-conveyed guns to perforating overbalanced with wireline-conveyed guns in moderate-to-high permeability core samples. Results were then compared to case history data to validate damage mechanisms in field injection processes and to develop understanding of how the design of perforation and completion processes in sand control, stimulated and injection wells could be optimized.

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