PetroChina key exploration domains: geological cognition, core technology, exploration effect and exploration direction

On the basis of the third evaluation on hydrocarbon resources and the distribution estimation of remaining oil/gas resources, PetroChina puts forward four key exploration domains, which are litho-stratigraphic reservoirs, foreland thrust belts, middle and lower combinations of the superimposed basins, and hydrocarbon-rich depressions or plays in the mature exploration areas. The litho-stratigraphic reservoir has become the main body of the reserves growth; the foreland thrust belts are the important domains for finding significant discoveries, the middle and lower combinations in the superimposed basins have increasingly important status in increasing geological reserves, and the fine exploration in hydrocarbon-rich depressions or plays also have prodigious exploration potential. The remaining hydrocarbon resources are mainly distributed in seven domains, which are large-scale litho-stratigraphic reservoirs, hydrocarbon-rich depressions (plays) in rift-subsidence basins, foreland thrust belts, middle-lower combinations in the superimposed basins, onshore new exploring areas and new basins, south areas of South China Sea, and unconventional resources. Among them, the former four domains have great exploration potential and are the important areas for reserves and production growth, and the latter three domains are the important fields of realizing resources strategic relay for PetroChina in the future. Key words: PetroChina, exploration domain, geological cognition, key technique, prospecting thought, significant discovery, exploration directio

Formation and distribution of volcanic hydrocarbon reservoirs in sedimentary basins of China

Volcanic hydrocarbon exploration in China has experienced three phases: accidental discovery, local prospecting, and all-round exploration. There are mainly Carboniferous-Permian, Jurassic-Cretaceous, Paleogene-Neogene volcanic rocks and lava, pyroclastics, and karst reservoirs in the oil- and gas-bearing basins in China. Volcanic rocks cannot generate organic hydrocarbons, and the combination of volcanic rocks, source rocks, and seals are the key controlling factor of the primary lava plays. The near-source play is most favorable for hydrocarbon accumulation. Distribution of oil and gas is controlled predominantly by the hydrocarbon generating center. The play requires communication with faults or unconformities. Near-source plays are in the faulted basins in eastern China. Structural-lithologic hydrocarbon reservoirs are formed in the higher place of faults and lithologic hydrocarbon reservoirs are formed on the slope. Two types of plays are developed in central and western China. The near-source play is most favorable for the formation of large stratigraphic hydrocarbon reservoirs. Key words: volcanic reservoir, eruption environment, volcano-deposition tectonic sequences, controlling factor

Division and evaluation of oil-gas prolific zones for litho-stratigraphic reservoirs in the Nanpu Sag

The Nanpu Sag is a typical lacustrine downfaulted hydrocarbon-rich depression. Some litho-stratigraphic reservoirs have been discovered in recent years. Based on “Sag-wide Oil-Bearing Theory” and petroleum system, the concept of “play” is used as a unit for the division and evaluation of oil-gas prolific zones in this paper. The overlaying technique of “four maps”, which are the fault structure map, the sedimentary facies, the major effective source-rock distribution map, and the current exploratory situation map, is applied to the comprehensive evaluation of oil-gas prolific zones. The Nanpu Sag in vertical is divided into three first-order plays, namely, above-source play, in-source play, and below-source play, and each of them can be subdivided into second-order plays. The above-source play is divided into eight oil-gas prolific zones and four favorable areas are evaluated. The in-source play is divided into five oil-gas prolific zones and four favorable areas are evaluated. The below-source play is divided into two parts with ten oil-gas prolific zones and five favorable areas are evaluated. Key words: Nanpu Sag, litho-stratigraphic reservoir, play, zone division: zone evaluatio

Geological features and evaluation techniques of deep-seated volcanics gas reservoirs, Songliao Basin

Abstract: The significant breakthrough of natural gas exploration in deep-seated volcanic rocks of Songliao Basin, China, demonstrates that the volcanic rocks as reservoirs can form natural gas accumulations where excellent source–reservoir–caprock assemblages exist. This paper reveals several features of volcanic gas accumulations: (1) Two types of gas reservoirs, including hydrocarbons and non-hydrocarbons, are developed; the former is organic and usually trapped in shallower volcanics associated with sub-deep-seated faults, while the latter is mainly inorganic and accumulated in deep-seated volcanics associated with large-scale deep-cut basement faults. (2) Lower Cretaceous Shahezi Formation coal series source rocks, Yingcheng Formation volcanics, and Denglouku Formation mudstone form good source–reservoir–seal associations that control the major volcanic plays. (3) Volcanic crater and eruptive facies spread along deep-seated faults, so discordogenic faults control the distribution of large-scale volcanic gas reservoirs. (4) Fracture zones, accompanied with large-scale faults, control the distribution of high-yield zones. (5) Effusive volcanic rocks in the deep parts of sags have huge thickness and touch extensively with source rocks, so the gas accumulation potential is promising if reservoirs exist. Evaluation techniques can be summarized in three steps: (1) Determining the distribution of volcanic rocks by joint inversion of gravitational, magnetic, and seismic data. (2) Predicting the distribution of volcanic reservoirs by multiple methodologies. (3) Predicting the distribution of gas-bearing volcanic rocks by integrated methods, including gas detention. Key words: Songliao Basin, deep layer, volcanic gas reservoir, pool-forming features, evaluation techniqu

Genesis, classification, and evaluation method of diagenetic facies

Based on the controlling of diagenesis and diagenetic facies on reservoir development, this article discusses the formation, classification, and evaluation of diagenetic facies and its application and significance in petroleum exploration. For constructive diagenetic facies such as clastic rock, carbonate rock, and igneous rock, eight kinds of genetic mechanisms are developed, including dissolution of organic acid, dolomitization, and so on. Nine constructive diagenetic facies and seven destructive diagenetic facies are classified. A naming scheme for diagenetic facies is proposed reflecting lithology, diagenesis, porosity, and permeability, that is, “porosity and permeability level + rock type + diagenesis type”. Diagenetic facies are evaluated synthetically and quantitatively on the basis of sedimentary facies, log facies, seismic facies, rock cores, and thin sections, and “four steps” and “superposition of three charts” are put forward as the methods of evaluation and mapping. Favored reservoirs, “sweet spots”, and lithostratigraphic traps can be predicted according to the distribution of different types of diagenetic facies. The development of the study on diagenetic facies is also discussed in the article. Key words: diagenetic facies, formation mechanism, classification and naming, evaluation method, petroleum exploration, diagenetic stud