Formation Damage vs. Solid Particles Deposition Profile during Laboratory Simulated PWRI

Abstract

Abstract The importance of produced water re-injection (PWRI) is unquestionable. It is in many cases the cheapest and most environmentally friendly solution for wastewater disposal. It is also a feasible method for EOR as a water flooding mechanism. PWRI, however, suffers from a major limitation, which is the current inability in accurately predicting the lifespan and performance of its injection wells. This is due to the multitude of parameters that affect it. Current models1–2 exist that incorporate the thermal effects3 of PWRI leading to fracture growth. However, the leak-off pattern of this injection differs from that of clean water (seawater) injection due to the damage caused by the produced water onto the formation and especially the fracture faces. Thus, static filtration experiments with refined post-mortem analysis have been conducted to obtain quantitative deposition profiles along the core. This allows for the testing and verification of existing models4–7. The post-mortem analysis introduced in this paper will be used for future dynamic filtration experiments as well as experiments specifically devised to simulate the fracture tip area. A unified model that will accurately reproduce the permeability decline and deposition profile for all three sets of experiments will flow, thus advancing the predictability of injectivity decline associated with PWRI. A detailed description of the post-mortem analysis will be presented. Testing of existing heuristic models Wennberg5 and Bedrikovedski7 will be published in the near future. Introduction Produced water re-injection (PWRI), when first introduced, was seen as a breakthrough solution for water disposal. It is both environmentally friendly and economically among the cheapest options. Thus, it garnered much interest. However, the associated injectivity decline remains a major issue. In order to simulate and predict the extent of formation damage inflicted by produced water re-injection it is necessary to have a competent model of the damage inflicted as a function of injection flow rate and particle concentration among other parameters. Different models exist in the literature - each having their merits and weaknesses. Thus, the authors of this article undertook controlled static filtration experiments with the addition of detailed post-mortem analysis. The post-mortem analysis is a new development that presents quantitative data that can be used to affirm or refute the predictions of existing heuristic models; thereby lending a guiding hand to the direction modelling should follow. The static filtration experiments were conducted using a 5-port sleeve, to obtain six pressure drop data channels over a 5.0 inch Bentheim sandstone core of 1-inch diameter. Bentheim sandstone is homogeneous with a porosity of 22%, permeability of approximately 1.4D and pore throat diameter of 10–15 (m. Distilled water containing 0.1 µm - 5 (m hematite (Fe2O3) particles (65% of which were less than 1 (m in diameter) was injected at different concentrations (20 ppm, 40 ppm and 80 ppm) and flow rates (5.4 l/hr and 10 l/hr) into the core - each experiment having only one injection concentration and one injection flow rate. The concentration of the effluent solution of the experiment was either measured online using a laser diffraction unit (Figure 1) or by collecting samples and quantifying the concentration at a later stage using chemical analysis (Figure 2). The data gathered used the guideline suggested by Wennberg8 as a compliance criterion. The post-mortem analysis consisted of quantitative visual analysis of core cross-sections as well as quantitative chemical analysis. Using these two techniques an accurate deposition profile of the injected solid along the length of the sandstone core was obtained. These two techniques will be discussed in detail in the next section.