Restimulation: Candidate Selection Methodologies and Treatment Optimization

Abstract

Abstract Restimulation of existing wells represents a vast underexploited resource. A successful refracturing treatment is one that creates a fracture having higher fracture conductivity and/or penetrating an area of higher pore pressure than the previous fracture. Refracturing requirements are different in highly permeable formations (high fracture conductivity) as compared to low permeable ones (moderate fracture conductivity). Understanding these basic differences is essential to a successful restimulation. In the past, candidate selection methodology has focused on underperforming wells. This simplistic approach has yielded disappointing results and has led to a common misconception that restimulations "don't work." Production statistics of a well alone may not offer an effective restimulation candidate selection methodology. Other parameters such as high BHP (remaining reservoir energy), recoverable reserves, f-h1 and favorable response to original fracture jobs (IP) could play an equally important role, if not greater, in determining the success of restimulation. In fact, studies have shown that selecting poor or underperforming wells for restimulation is likely to result in worse outcomes than random selection of workover candidates. Studies performed to date have concluded that no selection criteria can be universally applied to every situation; rather that the selection methodology for workover candidates must be customized to fit particular situations. This paper explores the common traits shared by fields likely to have underexploited restimulation potential and suggests methodologies that should be applied to various field types. The case histories illustrated in this paper will highlight the various treatment parameters optimized for successful restimulation. The conclusions of this paper are based on our work in selecting restimulation candidates as well as published results of other operators. Application of the correct candidate selection methodology to a particular field type will inevitably lead to a higher success rate of restimulation walkovers and the capture of an underexploited resource. Introduction Selection criteria of refracture candidates from a given set of wells in a field will vary depending on the reservoir under question and the prevailing well conditions. To be successful, refracturing treatments must result in longer and/or more conductive propped fractures, or expose more net pay thickness to the wellbore (establishing linear flow into the wellbore) as compared to the well conditions that exist prior to restimulation. In light of the above, two key important aspects of any restimulation program or attempt are:learn from existing experience in the field or area about restimulation and formulate a reservoir specific selection criteria that will capture the key ingredients for the success of restimulation anda thorough understanding of the treatment parameters that govern the success of a restimulation job so as to be able to optimize the treatment for maximum rate of return. Advances in the design and evaluation software, improved diagnostic techniques, etc, have played a key role in restimulation success during the past ten years, as have the technological advances in stimulation fluids and proppants. This paper will focus on the common attributes shared by known successful restimulation candidates in the industry. An attempt will be made to highlight the attributes mentioned in this paper through some well-known case histories. Based on the existing knowledge base on the restimulation identification process, a systematic and comprehensive candidate selection methodology will be presented in this paper. Towards the end, a list of factors to look for while evaluating a field or reservoir for restimulation will be highlighted for reference.