Hydraulic fracturing is a commonly used completion approach for extracting hydrocarbon resources from formations, particularly those of very low permeability. As part of this process diagnostic fracture injection tests (DFIT) provide valuable information. When the measured pressures in such tests are outside the expected range for a given formation, a number of possibilities and questions arise. Such considerations may include: What caused such inflated pressures? What is the in-situ stress state? Was there a mechanical or operational problem? Was the test procedure or the test equipment at fault? What else can explain the abnormal behaviour? While there may not be simple answers to all of these questions, such an experience can lead to a technically inaccurate conclusion based on inadequate analysis.
A recently completed project faced such a challenge, initially resulting in poor hydraulic fracturing efficiency and a requirement to understand the root cause. In support of this a thorough analysis, involving a multi-disciplinary review team from several technical areas including petrophysics, rock/geo-mechanics, fluids testing/engineering, completions engineering, hydraulic fracture design and petroleum engineering, was undertaken. This paper describes the evolution of this study, the work performed and the results and conclusions from the analysis.
The key factors involved in planning for successful DFIT outcomes are highlighted and a general template and work process for future testing has been provided. The limitations of using DFIT tests for planning the main hydraulic fracturing operations are discussed. The importance of appreciating the impact of the drilling and completion fluids composition, properties, compatibility with formation fluids are addressed. The overall process and technical approach from this case study in tight gas fields, will have applicability across similar fields and the lessons learned could help unlock reserves that are initially deemed technically or even commercially unattractive due to abnormal pressures measured via DFIT.
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