Abstract
Sandstone oil reservoirs consist of different clay minerals such as kaolinite, illite, and chlorite. These clay minerals highly affect the formation damage during enhanced oil recovery (EOR) and well stimulation operations in these reservoirs. No attention was paid to investigate the effect of these clay minerals on the formation damage during different reservoir processes. In addition, no solution was introduced to mitigate the effect of clay minerals on the formation damage in sandstone reservoirs. In this study, the effect of clay mineral contents and type on the formation damage was studied in detail by injecting water and HCl as damaging fluids. Bandera grey, Berea, and Bandera brown sandstone rocks with various clay mineral contents were studied. XRD was used to characterize the sandstone rocks to determine the clay type and content in each rock. Two core plugs from each rock were selected for HCl and water injection. Core flooding experiments were performed to measure the initial and final permeability. In the core flooding experiments, fluids were injected into the cores at 25 °C and at a backpressure of 1000 psi. SEM was carried out before and after flooding for the tested rocks to locate the change in the clay distribution inside the rocks. The NMR analysis of core samples was done before and after flooding with the damaging fluid to quantify the formation damage and to find the possible damaging mechanism. NMR was used to locate the damage inside the rock due to the migration of clay minerals. Based on the core flooding, SEM, and NMR analysis, the maximum damage by the fresh water took place in Berea sandstone core due to fine migration and clay swelling. The illite clay mineral and chlorite can cause the formation damage on HCl injection. Illite can break down and migrates in the cores during the acid injection. In sandstone acidizing, chlorite clay mineral caused iron hydroxide precipitation inside the cores during treatment with mud acid. NMR showed that clay minerals plugged the pore throats of the rocks and reduced the rock permeability during the injection of fresh water.
Highlights
Formation damage is attributed to many processes such as drilling, completion, acidizing, and enhanced oil recovery (EOR)
The objectives of this study are to evaluate the damage caused by different clay minerals in sandstone rocks during stimulation and enhanced oil recovery processes using core flooding, NMR, and Scanning electron microscope (SEM) analysis
The mineral composition analysis reveals that Bandera Grey sandstone core contains 3 wt% kaolinite and 10 wt% illite
Summary
Formation damage is attributed to many processes such as drilling, completion, acidizing, and enhanced oil recovery (EOR). The precipitation of organic and inorganic materials may result in a reduction in the production or plugging the well. Inorganic scales such as CaCO3 and C aSO4 are of the most common well-plugging conditions which occurs within the tubing string. Organic scale materials such as paraffin could precipitate near the well or inside the wellbore. Different polymer additives used in drilling, completion and EOR could reduce the permeability due to plugging in pore throats of the rock (Audibert et al 1999)
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