A Simple Method for Identifying Fracture Initiation Pressure

Abstract

Abstract A reliable interpretation of Fracture Initiation Pressure (FIP) provides key information for both efficient well planning and construction. With the trend towards drilling ever deeper offshore wells, depleted zones and more complex well paths, the available mud weight window continues to tighten, so an improved knowledge of the FIP becomes essential in enabling robust designs and risk reduction strategies that together promote safe and efficient operations. A number of methods are currently used across the Industry to estimate FIP values for drilling and completion applications. These methods involve the direct interpretation of data from injection tests, such as Diagnostic Fracture Injection Tests (DFIT), Formation Pressure Integrity Tests (FPIT) or even Wireline Formation Tests (WFT). In this paper, the authors propose and present a simplistic yet effective approach to derive values for the FIP from such typical pumping test data. The method is based on long established principles linking the pressure, volume and in-situ rock properties of the system being tested. This paper provides a number of examples to demonstrate the application and validity of the approach, including the consideration of scaled laboratory block tests, through to actual field data. The relationship between FIP, FBP and closure pressure is presented and discussed for all of these cases. The method is based on early-time wellbore stiffness considerations and as such complements and augments the more conventional fracture closure analysis approach from decline data. Using this technique, additional valuable information may be extracted even from only partially completed tests, where formation breakdown analysis by conventional means may either be impossible to perform or at best is somewhat inconclusive. In summary, while there are many and varied techniques that have been widely developed in support of obtaining FIP, the quality, the repeatability and assurance of these approaches is often incomplete and can sometimes be misleading. The simplistic methodology that is outlined and presented here provides a complementary approach, with the potential to offer a more consistent estimation of this key pressure control parameter. The method also provides the possibility of identifying the FIP in those situations where the currently available data (quantity and/or quality) would suggest that conventional methods might well fail to deliver an unbiased interpretation.