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SOCkAU of Petroleurn Engineers SPE 16798 Systematic Design and Analysis of Step-Rate Tests To Determine Formation Parting Pressure by P.K. Singh, R.G. Agarwal, and L.D. Krase, Amoco Production Co. SPE Members Copyright 1907,Society of Petroleum Engineers This paper was prepared for presentation at the 62nd Annual Technical Conference and Exhibition of the Society of Petroleum Engineers held In Dallas,TX September 27-30,1987. ■/�■ This paper was selected for presentation by an SPE Program Committee following review of information contained In an abstract submitted by the author(s).Contents of the paper,as presented,have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the •Y\ i//• authof(s).The material,as presented,does not necessarily reflect any position of the Society of Petroleum Engineers,Its officers,or members.Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers.Permission to copy Is restricted to an abstract of not more than 300 words.Illustrations may not be copied.The abstract should contain conspicuous acknowledgment of where and by whom the paper Is presented.Write Publications Manager,SPE,P.O.Box 633836,Richardson.TX 75083.3836.Telex,730989 SPEDAL. ABSTRACT Determination of FPP is of critical importance for efficient operation of waterfloods and tertiary Step rate testing (SRT) has been used for sev- recovery projects. Injection above parting pressure eral years to determine the formation or fracture can result in premature breakthroughs, poor sweep, parting pressure (FPP). Unfortunately, little is reduced oil recovery, and loss of costly injection available in the literature regarding SRT design and fluids due to uncontrolled fracture extension. On analysis. Further, the available guidelines are the other hand, injection at pressures far below the inadequate and may lead to questionable values of FPP implies injecting at a lower rate than an allo- the FPP. wable maximum and thereby a reduced rate of oil recovery. A systematic investigation of several signifi- cant factors affecting SRT design and analysis is Unfortunately, technology development in the presented. The analysis of SRT data influenced by area of step rate tests has not kept pace with field wellbore storage and changing wellbore storage is operations even though these tests have been common investigated. The proper application of multirate place in our industry for over 40 years. This is analysis methods to SRT data is outlined. A new reflected by a surprising lack of references in the method is proposed for determining parting pressure literature on the subject and continued problems from SRT data on fractured wells. Field examples with the interpretation of such tests. To our are included. This work should significantly knowledge, there have been only two papers published enhance our ability to successfully design and ana- in the literature,213 which directly address step lyze Che step rate tests. rate test (SRT) design and analysis. A brief dis- cussion is also presented in SPE Monograph 5.4 Our INTRODUCTION investigation shows that the previously available guidelines are inadequate and may lead to question- Step rate testing (SRT) is the primary method able values of the FPP. used to define the maximum safe injection pressure without fracturing the reservoir rock. This pres- The entire subject of multiple rate flow into sure is referred to as the formation or fracture the reservoir during a SRT, coupled with reservoir parting pressure (FPP). It is the pressure that fracturing, is a complex one since it requires a will initiate a fracture in an unfractured well or knowledge of both rock mechanics and fluid flow will extend an existing fracture in a fractured aspects of the problem. A recently published paper well. The "FPP" determined from step rate tests is provides some understanding regarding waterflood equivalent to the term "fracture extension/ induced fracture propagation.5 The analysis of SRT propagation pressure" used in the hydraulic frac- data is also subject to the type of problems which turing literature.) The FPP is generally greater are common to other pressure transient tests. than the "closure pressure" (defined as the pressure required to initiate the opening of an existing This paper presents (1) a discussion of the fracture) determined from pump-in/flowback tests.) test procedure and the theoretical basis for the conventional and multirate analysis methods; (2) the influence of several parameters such as time step duration, rate increment, wellbore storage, and changing wellbore storage on test data; (3) the References and illustrations at end of paper. 491