Oil and gas fields encounter issues associated with clay minerals through drilling and production. Depending on the types of clay minerals, they pose the danger of swelling and migration upon exposure to incompatible water. Drilling introduces water through drilling mud, and production introduces water through different treatments such as acid stimulation and hydraulic fracturing.The recovery of oil and gas from subterranean formations has been troublesome in formations that contain water-sensitive minerals, e.g., water-swellable clays, such as clays in the smectite group, and fines capable of migrating when disturbed, such as silica, iron minerals, and alkaline earth metal carbonates.It has been common practice to add salts to the treatment fluids. The salts adsorb to the clay surfaces in an ion exchange process that can temporarily reduce the swelling and/or migration of the clays. Another method used is to coat the area with a polymer in order to physically block the surface of the clays. This paper will mention the types of clays related to the oil industry, describe the structure of clays, mention the mechanisms behind swelling and migrating, and compare the different developments in the field of clay inhibition.
The increasing demand for energy has extended the development horizon towards relatively tighter formations. However, experience has shown that the most successful technique to optimize production from these tight carbonate formations would require multistage acid fracture stimulation treatment. Generally, laboratory tests, computer simulation and technical expert opinions yield optimistic results which are not always replicated in the field due to the absence of strong QA/QC follow-up. This field support was considered critical for a recent multi stage acid fracture treatment which involved many variables and fluid additives in an onshore Saudi Arabia multi-lateral well. This report will discuss the pre-job laboratory tests and fluid optimization process which included core flooding, compatibility, stability, and rheology tests. In addition, this paper will outline the QA/QC process adopted throughout the various operational stages and provide flowchart as recommendations for subsequent multistage acid fracture treatments in the field. Also presented is a case study from the first successful oil field multistage acid fracture treatment in Saudi Arabia. Laboratory results obtained reflected the negative impact of increased salinity on the crosslinked viscosity. In addition, a new low temperature-instant crosslinker was evaluated as an alternative which resulted in higher viscosity and faster break time. Further laboratory tests showed the sensitivity of the emulsifier used to mix emulsified acid and this led to corrective changes to the on-site mixing process. These and many other operational adjustments enabled bridging the gap between laboratory design and field implementation, thereby ensuring a successful acid fracturing treatment.
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