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The Karst Carbonate Reservoir and Its Exploration and Production

Abstract

Karst topography are widely seen and documented through the world. But karst reservoir in hydrocarbon exploration and production is not understood in the same level. When buried deeply, karst caves are generally considered being collapsed without much room left. But karst carbonate reservoir in Tarim Basin, West China tells a different story. Even buried underground more than 5000m deep, the karst caves developed 250Ma ago in Ordovician carbonates of Tarim Basin are still not collapsed. With tremendous storage spaces, they have produced huge amount hydrocarbons and become the importation drilling targets in Tarim Basin. Due to the extremely high heterogeneity of karst reservoir properties, seismic reservoir characterization has been applied as the main methods to analyse and predict reservoir and fluid types in karst carbonate. In seismic, large paleo karst caves are evident as strong amplitude anomalies. But drilling on them not only has led to many high productive wells but also been challenged by many dry and low-productive holes. To improve the drilling success, an effective approach has been developed in integrated study. 1. Recognizing the the main control factor for the production and reserves being the development and fluid content of karst caves. 2. Establishing the effective workflow including accurate seismic imaging of karst caves, detailed seismic interpretation on cavenous reservoir, reconition on karstification model to understang reservoir development and connectivity, and establishing effective approach to predict reservoir/fluid distribution. 3. Optimizing the drilling plan under the condition of high uncertainty and unevenly distributed reserves and the aim at high recovery and efficiency. This approach has been very effective in following E&P drilling, representing a breakthrough in both geological understanding and exploration techniques on karst carbonate reservoir. It not only provided the best practices in exploration on karst reservoir in Tarim basin and world but also valuable reference for the knowledge on karstification in earth history.