Abstract

This paper discusses the reservoir space in carbonate rocks in terms of types, combination features, distribution regularity, and controlling factors, based on core observations and tests of the North Truva Oilfield, Caspian Basin. According to the reservoir space combinations, carbonate reservoirs can be divided into four types, i.e., pore, fracture–pore, pore–cavity–fracture, and pore–cavity. Formation and distribution of these reservoirs is strongly controlled by deposition, diagenesis, and tectonism. In evaporated platform and restricted platform facies, the reservoirs are predominately affected by meteoric fresh water leaching in the supergene–para-syngenetic period and by uplifting and erosion in the late stage, making both platform facies contain all the above-mentioned four types of reservoirs, with various pores, such as dissolved cavities and dissolved fractures, or structural fractures occasionally in favorable structural locations. In open platform facies, the reservoirs deposited continuously in deeper water, in an environment of alternative high-energy shoals (where pore–fracture-type reservoirs are dominant) and low-energy shoals (where pore reservoirs are dominant).

Highlights

  • Carbonate reservoirs contribute about 60 % of the world’s oil and gas production

  • This paper discusses the reservoir space in carbonate rocks in terms of types, combination features, distribution regularity, and controlling factors, based on core observations and tests of the North Truva Oilfield, Caspian Basin

  • Many researchers have recognized that the carbonate reservoirs in the Caspian Basin are very complex in diagenesis and fracture formation (Wang et al 2012a, b; Zhao et al 2010, 2012; Xu 2011)

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Summary

Introduction

Carbonate reservoirs contribute about 60 % of the world’s oil and gas production. The Caspian Basin is one of the major petroliferous basins in the world, where over 90 % of the oil and gas production is from carbonate reservoirs. Taking the North Truva Oilfield in the eastern margin of the Caspian Basin as an example, based on core observations and tests, this paper discusses the features and genesis of pores, fractures, and dissolved cavities in carbonate reservoirs of open platform—evaporated platform facies. It gives a classification of the carbonate reservoirs according to the features of their reservoir space, describes their physical property features, and analyzes the distribution and combination regularity and controlling factors of different types of carbonate reservoirs

Types and genesis of reservoir space
B2 2500
Dissolved cavities
Features of reservoir space combination
Pore-type reservoir
Fracture–pore-type reservoir
Pore–cavity-type reservoir
Distribution regularity of reservoir types
Findings
Conclusions
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