Permeability natural fractures

Carbonate rocks are more frequently fractured than sandstones. In many cases open fractures in carbonate reservoirs provide high porosity / high permeability path ways for hydrocarbon production. The fractures will be continuously re-charged from the tight (low permeable) rock matrix. During field development, wells need to be planned to intersect as many natural fractures as possible, e.g. by drilling horizontal wells. 

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. 

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. 

Branagan, P.T., et al "Case History of Hydraulic Fracture Performance in the Naturally Fractured Paludal Zone The Transitory Effects of Damage," SPE paper/DOE 16397, 1987 SPE Low Permeability Reservoirs Symposium, Denver, May 18-19. 

N2 injection rapidly increases the methane production rate. The timing and magnitude depends on the distance between injection and production wells, on the natural fracture porosity and permeability, and on the sorption properties. N2 breakthrough at the production well occurs at about half the time required to reach the maximum methane production rate in this ideal case. The N2 content of the produced gas continues to increase until it becomes excessive, i.e., 50% or greater. 

Polak, A., Elsworth, D., Yasuhara, H., Grader, A.S., and Halleck, P.M. (2003) Permeability reduction of a natural fracture under net dissolution by hydrothermal fluids, Geophys. Res. Lett., 30(20), 2020,... 

Pyrak-Nolte, L. J., L. Myer, N. G. W. Cook, and P. A. Witherspoon, Hydraulic and mechanical properties of natural fractures in low permeability rock, Proc. Int. Cong. Im. Soc. R. Mechs., Montreal, 225-231, 1987. 

Zheng Shaohe, Zhao Yangsheng and Duan Kanglian, 1999, An experimental study on the permeability law of natural fracture uruler 3-D stresses, Chinese J. Rock Mech. Eng., Vol.18, No.2, pp. 133-136... 

THE EVOLUTION OF PERMEABILITY IN NATURAL FRACTURES - THE COMPETING ROLES OF PRESSURE SOLUTION AND FREE>FACE DISSOLUTION... 

Directional properties also occur in coal and these properties can affect the direction of flow of gases. For a particular coal seam, analyses of natural fracture orientation, directional permeability, directional ultrasonic velocity, and directional tensile strength (Berenbaum and Brodie, 1959 Ingles, 1961) may disclose distinct coal structures that are important for gas flow through the coal (Skawinski et al., 1991 Puri and Seidle, 1992). 

Danang, R. Widjaja, StigLyngra, FahadA. Al-Ajmi, etal. 2013. Vertical casedproducersoutperfonnhorizontal wells in a complex naturally fractured low permeability reservoir. SPE. 164414. 

In damage assessment, it is necessary first to find information on the reservoir geology, as well as the mineralogy. An understanding of the rock type (sandstone or carbonate) and other features, including permeability and porosity, is critical. This includes the nature of porosity (matrix versus naturally fractured) and how permeability is distributed (i.e., how it varies) across the producing interval—or the injection interval, as the case may be. 

Naturally, during injection, add takes the path of least resistance, as does any injected fluid. Anyone who has worked on acid treatment design or treatment execution has no doubt heard or said that before. The paths of least resistance will be those formation sections or layers with the highest permeability and the least damage. Higher-permeability streaks or natural fractures will accept fluid more readily than zones of lower permeability or injection capacity. 

Volumetric sweep efficiency is determined by the permeability and wettability distribution in the reservoir and by the properties of injected fluids. Waterflooding characteristically exhibits poor volumetric sweep efficiency. The more expensive the injection fluid, the more important it is to have a high volumetric sweep efficiency so that the injected fluid contacts and thus mobilizes a larger volume of oil. High permeability streaks or layers (thief zones) and natural or induced rock fractures can channel the injected fluid through a small portion of the reservoir resulting in a low volumetric sweep efficiency. 

Xanthan has several undesirable properties. It ordinarily forms microgel particles that can plug permeability(137), it is expensive relative to other natural polysaccharide gel agents, and it resists degradation by ordinary gel breaker additives. These features have kept xanthan applications in fracturing gels to a minimum. Some literature(138) on xanthan has appeared. 

Most of these reservoirs have natural permeabilities below 10 mD, and the stimulation of their production is achieved through acid fracturing operations. Viscosified hydrochloric acid is pumped into wells at pressures larger than formation parting pressure. Irregular etching of the fracture walls by the acid is expected to create highly... 

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