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Growth of stylolites may adversely affect the continuity of carbonate reservoirs by producing barriers to fluid flow. The impact of stylolite development on reservoir performance, however, may differ from one part of a reservoir to another. Therefore, for effective reservoir management, the distribution and the permeability of stylolite-bearing beds should be known. In an example from the Lower Cretaceous of the Middle East, 3 zones of stylolites (D1, D2, and D3) are important to reservoir management. Only the uppermost zone (D1) is a significant barrier to fluid flow. Because the impermeable zone (D1) formed largely before oil entrapment, local precipitation of calcium carbonate occurred at abundant crystal-nucleation sites adjacent to the stylolite zone. The other stylo ite zones (D2 and D3) were formed largely during or after oil entrapment. Oil inhibited carbonate precipitation by coating crystal nucleation sites. Calcium carbonate, dissolved at pressure-solution surfaces, was then transported away from stylolite zones prior to precipitation. Consequently, stylolites formed after oil entrapment do not constitute significant barriers to fluid flow.
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