Permeability damage

Figure 4-124. Effect of HCI on HEC on permeability damage caused by completion fluid [36], (Courtesy SPE.)...

B. L. Gall, D. R. Maloney, C. J. Raible, and A. R. Sattler. Permeability damage to natural fractures caused by fracturing fluid polymers. In Proceedings Volume, pages 551-560. SPE Rocky Mountain Reg Mtg (Casper, WY, 5/11-5/13), 1988. 

Foamed cement slurries have been used to provide a low density cement slurry to reduce permeability damage to highly sensitive formations through reduced fluid loss (29). Glass microspheres have also been used to substantially reduce cement slurry density (30, 31). Other additives which reduce cement slurry density to a lesser extent include bentonite, fly ash, silicates, perlite, gilsonite, diatomaceous earth, and oil emulsions (see citations in reference 29). 

Fluid loss from the wellbore to the formation may be reduced using the less permeability damaging drilling fluid loss additives described above. In saturated brines, carefully sized sodium chloride particles have been used to temporarily plug the formation face (35). The particles may be dissolved by pumping a less saline fluid down the wellbore. 

Formation permeability damage caused by precipitation of dissolved minerals such as colloidal silica, aluminum hydroxide, and aluminum fluoride can reduce the benefits of acidizing (132-134). Careful treatment design, particularly in the concentration and amount of HF used is needed to minimize this problem. Hydrofluoric acid initially reacts with clays and feldspars to form silicon and aluminum fluorides. These species can react with additional clays and feldspars depositing hydrated silica in rock flow channels (106). This usually occurs before the spent acid can be recovered from the formation. However, some workers have concluded that permeability damage due to silica precipitation is much less than previously thought (135). 

Gall, B.L. Maloney, D.R. Raible, C.J. "Permeability Damage to Artificially Fractured Cores," NIPER- Final Report, National Institute for Petroleum and Energy Research, Bartlesville, OK, May 1988. 

Other minerals beside water-swelling clays have been found to undergo fines migration. The permeability damage caused by essentially non-swelling clays such as kaolinite and chlorite is a well-known phenomenon. Silica fines have been identified as a potential source of permeability damage in various poorly consolidated U.S. Gulf Coast formations (1). Other minerals identified as constituents of mobile fine particles include feldspar, calcite, dolomite, and siderite (4,5). 

Core floods were performed to determine if treatment polymers would prevent permeability damage caused by fines migration within consolidated rock and whether the adsorbed polymers would themselves reduce core permeability. The tests were performed using Hassler sleeve chambers. With the exception of the polymer... 

Fines production from untreated test sands and permeability damage observed in untreated cores indicated that the laboratory test flow rates were above the critical flow velocity required to initiate fines migration. 

Results indicated that swelling clay stabilizers such as poly (DMA-co-EPl) which do not possess a quaternary nitrogen atom in a pendant chain may not be very effective at preventing permeability damage due to fines migration in the absence of water-swelling clays. 

Berea core flood test results (Table VIII) suggested that the presence of DMAEMA improved the permeability damage characteristics of 80% NVP copolymers. The kerosene flow rate... 

TABLE VIII. PERMEABILITY DAMAGE CHARACTERISTICS OF NVP COPOLYMER MINERAL FINES... 

With the exception of saturated zinc bromide, all of the fluids tested minimized permeability damage relative to fresh water which reduced permeability an average of 54% for three cores. 

Although potassium chloride fluids performed better than the calcium and zinc halides, damage was still measurable. These results, confirmed in triplicate, were unexpected since it is well accepted that even 0.5 weight % KC1 should protect Berea cores against permeability damage. The most plausible explanation lies in variation between the test procedures. 

The formation brine used to establish the core s initial permeability contained 2.7% total dissolved solids, TDS, with a monovalent-divalent (calcium) ratio of 30. Once a core is equilibrated with this brine, any increase in the ratio or drastic decrease in TDS has the potential for decreasing permeability. Obviously fresh water represents a significant decrease in TDS and, hence, the 54% permeability damage. Adding KC1 helps overcome the decreased salinity but, in so doing, increases the ionic ratio resulting in still measureable but usually reduced permeability damage. 

Gall, B.L., et al. "Permeability Damage to Natural Fractures Caused by Fracturing Fluid Polymers," SPE paper 17542, 1988 SPE Rocky Mountain Regional Meeting, Casper, May 11-13. 

Other mechanisms for particle capture include particle settling, inertia, and hydrodynamics (I). When a particle is captured in a pore, the pore throat diameter is reduced by a factor dependent on particle size and pore throat diameter. The reduced diameter of the pore throat will lead to a lower permeability. Permeability damage due to flow of suspensions increases with particle size and solids concentration. 

Mobilization and Capture of Formation Solids. Permeability damage occurs also as a result of solids mobilized or precipitated in the formation, as explained earlier. Figure 13 shows the decline in per-... 

Figure 13, Permeability damage due to in-situ mobilized particles, (Reproduced with permission from reference 71, Copyright 1988,)...

The nature and properties of common clay minerals found in petroleum reservoirs are briefly discussed to set the stage for a review of the colloidal and hydrodynamic forces acting on the fine particles. This is followed by a review of reported experimental studies of permeability damage by fines movement under purely hydrodynamic forces. 

Experimental Studies of Permeability Damage by Mechanical Fines Migration... 

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