Simulation of Drilling Challenges in Pressurized Saltwater Disposal: A Case Study in the Williston Basin

Abstract

ABSTRACT: Water is produced along with the hydrocarbons from the Bakken and Three Forks formations in the Williston Basin. The water to oil ratio increases over time, with more water being produced as the formation is depleted further. Water needs to be managed, treated, and disposed of for production to continue. Salt water disposal into porous formations is a common practice in the Bakken, which is regulated for proper water injection and disposal. Studying the effect of the water injection and its impact on saturation/salinity, and change of formation pressure and in-situ stresses over time are some of the important aspects to be considered. This study investigated the effect of pressure increase around the saltwater disposal wells due to water injection. A total of 115 saltwater disposal wells were used in this study to model the Inyan Kara aquifer formation in the Bakken. The dynamic flow and 1D geomechanical models were built based on injection tests, build-ups interpretations, and historical injections rates in order to capture the historical performances of the aquifer over time. The aquifer pressure evolution over time was investigated at the location of current producing wells and at future potential drilling locations to reach the Middle Bakken and Three Forks reservoir formations. The results showed that the elevated pressure of the aquifer requires substantial increases of the mud weight to avoid shear breakouts and fracturing of the formation, which increases the risk of fracturing the Skull Creek formation above and Swift formation below the Inyan Kara. Also, the salinity difference is expected to cause barium sulfate and calcium carbonate precipitation and injectivity issues. No casing failure is expected for the cases that studied here as the pressure will not exceed the casing strength. 1. INTRODUCTION Hydrocarbons production is predominately associated with water production. Formation water is separated treated and disposed. The unconventional resources development in the Williston Basin was accompanied by a large amount of produced water. The amount of water is the same as the volume of produced oil. The produced water is then disposed through a network of salt water disposal wells, which are completed through the Dakota Group of formations mainly targeting the Inyan Kara formation.