Laboratory Procedures for Estimating the Impact of Solids and Oil-Emulsions Content in Synthetic and Real Produced Water on the Injection Pressure Drop Over Outcrop Sandstone Cores

Abstract

Abstract Produced water re-injection in hydrocarbon extraction is nowadays common practice mainly enforced by environmental concerns and regulations. Produced water contains, however, significantly higher levels of solids and oil emulsions than regular water used for injection purposes. The negative impact these constituents have on water injectivity has been known for a long time and documented in several publications as far back as the 1980s. Injectivity decline has in general also obtained increased focus over the last decades due to increased interest in CO2 injection for storage purposes as well as increased focus on reduced power consumption and emissions, all through the value chain. The topic is therefore closely linked to important issues related to environment, storage, power consumption, emissions, and economy. Decline in injectivity vs. time is hence expected when produced water re-injection is implemented but improved predictions for how it will evolve is important for reservoir management purposes. Since such predictions conventionally are generated using simulators, robust and reliable experimental input data is crucial. There are many publications focusing on performing controlled laboratory experiments and develop theoretical models to interpret the data. Generating experimental data in cases where the aqueous phase also contains solids and oil emulsions is, however, associated with significantly more challenges and higher uncertainties than conventional tests, which involve homogeneous fluid phases. They originate from the tendency both solids and oil emulsions have to segregate in opposite directions all through the test period. Such additional challenges may in worst case induce uncertainty levels preventing conclusions to be drawn. The aim of the current work focuses on the improvement and standardization of laboratory procedures and practices for mitigating the two major additional challenges related to segregation. They were established by performing numerous tests in several different laboratories using synthetic produced water with well-defined particles and oil emulsions added together with outcrop sandstone cores. The consequence could be increased reproducibility and reduced uncertainty in the final experimental results reported from such tests. The result is therefore a recommended practice list where each bullet point is described in detail sequentially as the test evolves. Additionally, some recommendations related to microbial issues are included if tests planned also include such challenges. Some experimental results are also included obtained using the practices and standards described. It is believed that the recommended practices contributed to increased reproducibility and reduced the uncertainty in all results including these. Increased emphasize on practices and standards for reducing the negative impact from lack thereof could perhaps also facilitate more inter-laboratory result comparisons in the future as they likely impact the results reported significantly.