Objective/Scope: Produced water chemistry provides an essential basis for risk assessment and management of water-related production issues including scale, corrosion, reservoir souring, field sludge formation, formation damage, etc. Produced water chemistry surveillance has also been recognized as a low cost and promising approach to help understand well connectivity/interference/drainage dynamics and improve decision making in shale asset development. This paper presents a comprehensive produced water chemistry surveillance study and its application in the Permian Basin.
Methods/Procedures/Process: Produced water chemistry surveillance over time were utilized to extrapolate formation water chemistry composition of the intended zone for landing and completion. Thousands of produced water samples were collected at wellhead and analyzed for ion concentrations and dissolved H2S. In consideration of various sources contributing to produced water at flowback/early production stage and potential well-well interference/connectivity, historical produced water chemistry data were integrated and reviewed to reliably assess the representativeness of individual produced water data for a well and understand the produced water chemistry evolution with time in different fields.
Results/Observations/Conclusions: In one study, produced water chemistry data from horizontal wells located at 5 different areas in the Permian Basin were studied. Formation water chemistry baseline dataset across different areas and formation depths was reliably extrapolated based on produced water chemistry surveillance. The analyzed ion concentration results show both vertical and horizontal water chemistry heterogeneity in the studied formation. Produced water ion concentrations from the same formation can vary significantly with the landing depth and geographic location. The study results show wells with 0.5 mg/L or higher H2S in produced water tend to appear in the same localized areas. Wells with negligible H2S in produced water in this study shows relatively low SO4 levels and high TDS (>100,000 mg/L). In a different study, produced water chemistry surveillance was designed and utilized to estimate frac water fraction in produced water from parent wells and proactively monitor fracture driven interaction (FDI)/in-situ well interference induced by hydraulic fracturing operations. Our study also shows low cost produced water chemistry surveillance can be used to differentiate waters produced from different formation zones, identify/allocate produced water source, provide insights to understand production performance and recovery mechanism, and assist well trouble shooting.
Applications/Significance/Novelty: For the first time in industry, we have demonstrated that formation water chemistry/salinity in shale reservoirs can be reliably extrapolated based on produced water chemistry surveillance and established vertical and horizontal heterogeneity understanding in formation water chemistry across different areas/depths in a studied shale formation in the Permian Basin. The improved understanding in subsurface heterogeneity and formation water chemistry can be utilized to improve OOIP determination and production source identification/allocation, as well as decision making and risk control in multiple aspects including but not limited to asset development, well completion, production operations, and produced water management/disposal.
