Techbits: China Workshop Examines Fractured Carbonate Reservoirs

Abstract

Techbits An SPE Applied Technology Workshop (ATW) on “The Characterization of Effective and Efficient Development of Fractured Carbonate Reservoirs” was held 15-18 June 2014 in Nanjing, China. Participants reviewed recent advances in exploration and production and the technical challenges presented by these reservoirs. A variety of carbonate reservoirs exist worldwide, mainly paleokarst reservoirs. Because of various scales, poor continuity, strong heterogeneity, accumulation in vugs and fractures, and complex flow behaviors, the efficient development of fractured carbonate reservoirs is quite challenging. Li Yang, cochairperson of the workshop, opened the session and ATW Chairman Wang Zhigang delivered one of two keynote speeches. He focused on the challenges and current activities of a key carbonate reservoir, Tahe, that he said represented the theme of the ATW. Usman Ahmed, also a workshop cochairperson, introduced the second keynote speaker, Christine Ehlig-Economides. She recalled an ATW a decade ago that also had focused on the Tahe reservoir. She set the stage for a discussion on how much the industry has advanced and the challenges that lie ahead. In his keynote speech, Wang of Sinopec described the technical challenges and techniques used at Sinopec’s Tahe oil field in western China. The Tarim basin is the company’s largest carbonate play, with proven reserves of 1.3 billion tons and depths of 5300 m to 6300 m. The oil and gas accumulated in pores, vugs, and fractures of severe heterogeneity and depth make it difficult to predict and describe reservoir characteristics, he said. Carbonate reservoir characterization and evaluation techniques have been developed that have improved the predictability of the carbonate reservoir and its distribution and have increased drilling success, he said. In the Ordovician carbonate reservoir of Tahe, a series of techniques such as paleokarst landform categorization, paleokarst cycle division, hydrocarbon accumulation period analysis, logging for reservoir identification, and evaluation have been implemented. In addition, massive acid fracturing (high pumping pressure, high injection rate, large scale) has become a major technique for development at the field. In sum, the technical challenges are: Ultradeep, highly heterogeneous reservoirs with low-resolution seismic data make it difficult for reservoir prediction. The form of fractures and vugs and oil and gas accumulation in such reservoirs make reservoir modeling difficult. A variety of reservoir fluid systems exist, which lead to a complex oil-water distribution. Current simulation techniques need to be further improved. Severe channeling and breakthrough were detected after waterflooding was applied. Further research is needed to improve waterflooding, residual oil characterization, and water-control techniques. Drilling activities are extremely challenging and costly. Drilling technology needs to be further developed or modified.