Ultrastrong Formations: Perforating Challenges, Limits, and Optimization

摘要

Due to high global demand, easy oil production is no longer sufficient to meet the continuous requirrements. Extracting oil by using enhanced recovery methods or from difficult environments poses many challenges that differ from one field or formation to another. Ultrahigh-strength formations present a particularly difficult environment. In addition to posing drilling challenges, such formations introduce significant challenges to completiion operations-particularly perforating and hydraulic fracturing, which represent the critical final steps in establishing formation-wellbore communication. A key perforating parameter is the perforation tunnel depth of penetration (DoP). A new paradigm of DoP modeling relies on shaped charge characterization in the laboratory under a range of rock strength and stress; however, most available data are for rock strength or unconfined compressive strength (UCS) values of less than 18,000 psi. Therefore, uncertainty exists regarding DoP in some Oman formations in which UCS varies from 20,000 to 55,000 psi. Two main phenomena need to be verified. First, because penetration is inversely proportional to UCS, extrapolation of the existing shaped charge performance data suggests that the penetration will be close to zero at this extreme rock strength. Second, characterization of the shaped charges under this new paradigm shows that a shaped charge that performs better in a weaker rock may not necessarily perform better in stronger rocks. Therefore, tests are needed to identify thhe optimal charge(s) in these very strong rocks. With these objectives in mind, cores obtained from the ultrastrong Amin formation in Oman underwent laboratory testing. Performance results of a series of tests designed in general agreement with the procedures of the American Petroleum Institue Recommended Practice (API RP) 19B Section 2 exceeded expectattion based on extrapolation of previously available laaboratory data. These new data provide valuable calibration points for the penetration model in ultrahigh-strength rocks. This paper presents the methodology, results, and observations of thiis test program and discusses the way forward, which should add value to perforation performance not only in Oman, but also worldwide in ultrahigh-strength formations. Although previous studies have briefly addressed high-strength formations, this is the first known work that systematically evaluates perforator performance in ultrastrong formations.