Determining Key Reservoir Parameters from Diagnostic Fracture Injection Test DFIT Conducted in a Disposal Well in the Bahrain Field Using Multiple Analysis Techniques

Abstract In the Bahrain field, wet sand waste/sludge mixtures generated from the Waste Management Sump Facility (WMSF) are stored in temporary storage areas. A well in a sandstone reservoir is identified for conversion to water disposal for waste management to dump around 3,000 barrels of NORM (naturally occurring radiative material) waste accumulated over the last 5 years. Estimating formation breakdown pressure and reservoir flow capacity is crucial for injection capacity estimation and safe injection in a disposal well. Step-rate test (SRT) and injection falloff have now become the standard practice to estimate formation breakdown pressure, reservoir pressure, and formation permeability. This paper focuses on the preparation of a NORM injector after a detailed review of geological, petrophysical, production, and reservoir engineering data of the sandstone reservoir in the field. An injectivity test using SRT followed by a pressure falloff test was conducted in the subject well to determine the injection rates and pressures required for injection of NORM waste. The paper presents the results of the step rate test (SRT) and both the before-closure and the after-closure analysis (ACA) of the falloff test conducted on the disposal well prior to design of SFI (slurry fracture injection process). Besides conventional analysis, the SRT is analyzed using modified-Hall analysis (MDH) and injectivity analysis. In addition, two rate and multi-rate (injection) analysis methods are also used for unambiguous interpretation of the data. Both pressure-derivative and G-function analysis are used to analyze DFIT data in order to evaluate fracture-closure pressure. Other parameters obtained from ACA are instantaneous shut-in pressure (ISIP) and fracture efficiency. The log-log derivative plot confirms the presence of the late-time pseudo-radial flow regime. Pseudo-radial flow analysis by different methods are used to determine reservoir permeability and initial reservoir pressure. Based on the analysis, it is inferred that reservoir is of good permeability as observed in high injection rates and corroborated by high permeability estimated from the radial-flow plot of ACA. The fracture breakdown pressures determined by conventional, two-rate and multi-rate analysis methods are supported by both modified-Hall and injectivity analysis. Fracture-closure pressure obtained from G-function, square-root, and derivative analyses compare favorably. Initial reservoir pressure and formation permeability estimated by different techniques are in good agreement, thus instilling confidence into the analysis. The multiple techniques described here can be used for comprehensive and credible analysis of SRT as well as before-closure and after-closure analysis of falloff data in a disposal well