Innovative Method for Predicting Downhole Pressures During Frac-Pack Pumping Operations Facilitates More Successful Completions

Abstract

Pressure limitations often prohibit engineers from placing frac-pack sand-control treatments where they are needed the most because of the collapse ratings of the bottomhole assembly equipment. Often, these pressure limitations lead to early abandonment of the well, or they create problems later in the life of the well, because they do not allow for effective sand-control, which inevitably will have a negative impact on well economics. A new method, dynamic pMAX, used to determine the amount of pressure exerted on the bottomhole tools during the sand-control treatment, enables frac-pack treatments that the industry once would have considered impossible to achieve. Introduction Sand control methods were first implemented in order to control the flow of fines during the production of hydrocarbons. Initially, fines control was limited to stand-alone screens and consolidation treatments; however, as technology progressed, new methods of sand control were attained.1 The most notable of these new methods was the frac pack, which became commonplace in the late 1980s and early 1990s for completing formations with high permeability. Frac-packs provide long-term stimulation similar to hard-rock hydraulic fracturing treatments, and they control the encroachment of small sand particles from "soft" formations.2 Although the frac pack could provide the capability to stimulate the formation as well as control the formation fines, high flow rates often induced proppant flow back. This problem was best solved through the use of downhole tools. Unfortunately, pressure limitations for the tools could impose limits on the types of sand-control jobs that could be pumped, and when modeling the maximum pressure for each job, planned frac packs had to be cancelled due to the pressure restrictions. Early jobs had encountered problems with collapsed components, primarily with the lower casing extension and the blank tubing. Engineers determined that the collapse ratings of these components were exceeded when a "hard" pressure screenout, which is one that occurs at fracturing rates and is desirable in a soft rock environment, was achieved.3 The "hard" screenout occurs after a tip screenout event and when the fracture is completely full of sand or proppant. The pressures seen during a "hard" screenout can rise excessively above the anticipated treating pressure in a short period of time, leading to unpredicted stress on the downhole assembly. During this time, it was assumed that building more robust equipment components was easier than attempting to predict what was actually going to occur; however, the excessive pressures could not always be anticipated. With a new method that has recently been developed, it is now possible to determine how much pressure can be encountered before the job is run. This method, known as pMAX prediction, allows the tool assembly to be designed with the expected pressures in mind. Bottomhole Assembly Review To fully comprehend the effects of pressure on the bottomhole tools necessitates an understanding of how the assembly for a sand-control completion is arranged. This knowledge will help the job designer not only recognize how pressures can be detrimental to job placement, but also how this pressure, when used in the proper manner, can help to put the frac-pack in place. The completion can be broken into two segments for easier understanding: the upper completion and the sand face completion. This paper focuses on the sand-face completion.