中国岩溶

foreword

Editorial Office of CASOLGICAL SINICA

2015, 34(2): 97-97.

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Scientific innovation in karst resources and environment research field of China

YUAN Dao-xian

2015, 34(2): 98-100. doi: 10.11932/karst20150201

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In karst areas of China, the natural resources and environment have some serious problems, which constrain the development of social economy. The Central Government has promoted the scientific and technical innovation and ecological civilization construction vigorously since the Eighteenth National Congress of Communist Party of China. Scientific and technical innovation can not only helps to face and solve the resource and environment problems in karst areas, but also promote the development of karstology, and provide service to the ecological civilization construction. The research on karst in the future should concentrate on the following aspects: to implement the application of earth system science in karstology, exert the regional advantages of China on the karst research, and explore the characteristics and significant processes of critical zones in karst areas of China; strengthen the research on the response of karstification to global change, the rate of carbon cycle and stability, and establish the permanent mechanism towards extremely climate; consider the influence of paleo-magnitude and paleo-climate on paleo-karst; explore deeply the functions of microbes to the formation of carbonate rock; summarize systemically the experiences and problems of the first phase improvement project on rock desertification control in China, in order to better guide the control work in the next step; pay attention to the declaration of karst natural heritage in terms of the karst boundary between north and south; apply the big data technology to the karst resources and environment as well as hydrogeological research, improve the warning and forecast research on geological hazards, and the research on the shortage of resources to serve our country. 

Evaluation of capacity and suitability of CO2 geological storage in carbonate formations in basins of China mainland

WANG Jing-xia, LEI Lei, YU Qing-chun

2015, 34(2): 101-108. doi: 10.11932/karst20150202

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Geological storage of carbon dioxide is one of the effective techniques to reduce CO2 emissions. Evaluation of capacity and suitability of such storage can provide a scientific foundation for policies of reducing greenhouse gas emissions. This work collects and analyzes the relevant data from the studies of petroleum geologyand engineering and hydrogeology. The porosity and thickness of carbonate formations in the basins of China mainland are investigated. A series of important geological maps related to CO2 storage in carbonate formations in these basins are prepared, including the “Classification map of areas of carbonate formations in the basins of China”, “Classification map of thicknesses of carbonate formations in the basins of China”, “Classification map of porosities of carbonate formations in the basins of China”, “Classification map of CO2 storage capacity of carbonate formations in the basins of China”, “Classification map of suitability of CO2 storage in carbonate formations in the basins of China”. After suitability evaluation and removal of those basins not suitable for CO2 storage, the basins with high suitability for CO2 storage are chosen for further investigation.

Types and models of supergene karst of Ordovician and reservoir characteristics in Ordos basin

SU Zhong-tang, LIU Na, YANG Wen-jing, HU Shang-cai, WU Chun-ying, PEI Wen-chao, REN Jun-feng

2015, 34(2): 109-114. doi: 10.11932/karst20150203

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Supergene karst reservoirs of Ordovician in Ordos is the most important type of carbonate reservoirs, while some breakthrough cannot be explained perfectly, indicating existence of different types of karst. Based on the analysis of paleotopography and cores and slices, this study suggests that the supergene karst of Ordovician can be divided into weathering crust karst and bedding karst，which include 4 subclasses in accordance with surrounding rocks. The characters of the weathering crust karst are different because of different rock fabric，while the easily dissolved component of rocks is dissolved preferentially when the bedding karst occurs. The weathering crust karst reservoirs are controlled by paleotopography and karst cycles as well as sedimentary facies, while paleotopography and sedimentary facies as well as grooves and fractures need to be considered when bedding karst reservoirs are forecasted.

Structural model and developmental characteristics of typical carbonate crack-cave systems under warm and humid climate conditions

CAO Jian-wen, XIA Ri-yuan, ZHANG Qing-yu

2015, 34(2): 115-125. doi: 10.11932/karst20150204

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1038

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Carbonate rocks can form typical crack-cave systems under warm and humid climate conditions. The Ordovician carbonate rocks has three tectonic uplifts in the Tarim basin, resulting in depositional break between Ordovician and Silurian, Carboniferous strata. The ancient Tarim land was located in low latitudes during the Devonian and Silurian, and had a tropical or sub-tropical climate which was favorable to generate large karst crack-cave systems. The Tarim area in Devonian and Silurian had the similar climate characteristics to the modern South China, and experienced intense karstification. Based on outcrops investigation and analysis of cores, seismic and logging data, combined with the modern karst theory, this work makes a comparative study and summarizes spatial structural characteristics of carbonate fracture-cave systems. Such typical systems under warm and humid climate conditions are divided into 4 types: underground rivers, karst caves, karst pores, karst seams. Furthermore, the underground river is subdivided into 3 sub categories of single pipe, multi pipe and corridor pipeline, and the cave is subdivided into the hall type, cave type and vertical type. Then eight corresponding structural models are established, and their characteristics are summarized. This will help to reveal the pattern of development and distribution of crack-cave systems in Tahe oil field, and provide a reliable basis for oil geological modeling.

Eogenetic karstification in carbonatite and its significance for hydrocarbon geology

DAN Yong, LIANG Bin, CAO Jian-wen, ZHANG Qing-yu, HAO Yan-zhen, LI Jing-rui

2015, 34(2): 126-135. doi: 10.11932/karst20150205

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Solution caves or big karst caves can be generated in carbonatite by eogenetic karstification, which is very important for the study of distribution and genesis of such caves in karst areas of the Tarim and Sichuan basins. However, young carbonate karst is few in amount and poorly studied in China. So, a large number of foreign literature about this issue were collected and reviewed in this paper. The purpose is to present features of the caves by eogenetic karst and their corrosion mechanism, and the petroleum geological significance. (1) Young carbonatite is characterized poor cementation, loose structure, and high porosity and permeability, with uniform medium space. (2) Eogenetic karst is obviously associated with rise and fall of sea level. Especially in islands or coastal areas with fresh-salt water interaction zones, the karstification featured by mixed water is relatively intense. (3) Holes or caves which formed by eogenetic karst have such patterns that flank margin caves develop in islands while channels of mixed zones appear in coastal karst. (4) Development of karst caves depends on the CO2 content of the freshwater, hydrological power of the mixed transition zone, and the change rate of sea level. (5) Eogenetic karst provides a theoretical reference for studying the short-term exposure of karstification during geological times. Such research will help understand formation mechanisms of hole-cave type carbonate reservoirs in internal karst areas and guide the distribution prediction of hole-cave type reservoirs in carbonatite regions.

Characteristics of imaging logging response and indication of paleokarst development in Lungu area

FU Hai-cheng, ZOU Chang-chun, XIAO Cheng-wen, QI Xing-zhong, WANG Ru-an, ZHAO Dan-ying, SUN Jian

2015, 34(2): 136-146. doi: 10.11932/karst20150206

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The Ordovician carbonate reservoir in the Lungu area of Tarim basin has been reformed by the superimposition of multi-stage tectonic movement and karstification. Primary oil and gas storage space can be found in the secondary pore structures, such as caves and fractures, formed by paleokarstification. Evaluation of karstification is an important area of research for evaluation of carbonate reservoirs. Based on processing of a large set of imaging logging data from the Lungu area, and mainly through analysis of the imaging logging response of caves and fractures, karstification rules are determined for the area. In imaging logging, a high conductivity fracture often manifests as a brown-black sine curve, generally with higher continuity; a corrosion fracture generally corresponds to a sine curve with irregular edges; a unfilled cave appears as dark clumps with local light colored clumps; additionally, fully filled caves, bedding and other sedimentary phenomenon can be observed in the resulting imaging logging map. The different levels of karstification can be identified by fractures and breccias in caves, which are interpreted by imaging logging. In western Lungu,the breccias in some large caves have been completely corroded and were filled with mud and sand, indicating a high level of karstification in this area. In central Lungu region, where some caves have greater amounts of breccia, the size of the cave produced by the corrosion of a single strike fracture is clearly smaller than that in western Lungu. This indicates weaker karstification in central Lungu compared with the western region. In eastern Lungu, small caves have not been produced by the corrosion of single strike fractures, only proto-caves or cross cracks and karst fissures can be observed by imaging logging. Statistical analysis of the number of caves in Lungu area indicates that the distribution of cave reservoirs is mainly affected by epigenetic karst zones.

Genesis relationship between faults and karst reservoirs in the Yingshan formation, Medieval No.8 wellblock

LI Jing-rui, LIANG Bin, YU Hong-feng, ZHANG Qing-yu, CAO Jian-wen, DAN Yong, HAO Yan-zhen, LI Jie

2015, 34(2): 147-153. doi: 10.11932/karst20150207

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There are abundant oil and gas resources in the Ordovician carbonate formation of the Tarim basin.The superposition and transformation in many episodes of different types of karst development are the main driving force of Tazhong ancient karst reservoirs. Faults are an important factor affecting karst reservoirs. The Medieval No.8 wellblock is situated in a northwest-southeast trending thrust fault zone of the Caledonian period and a northeast-southwest trending strike-slip fault zone of the Hercynian period, which form a network system. The karst reservoirs developed in the subsurface from the top of Yingshan formation to 120 km depth, which are of hole type, cavity type, fissure type and fissure-hole type. Of these, the fissure-hole type and hole-type are dominant. The multi-episode faults and associated fissure network system of the Caledonian to Hercynian period serve as good migration channels for fluids, which promote the development of the fissure-hole system, burial dissolution and dolomitization, improving the performance of reservoirs to become a complex combination of carbonate holes, cavities and cracks.

Reconstruction of karst palaeogeomorphology for the Ordovician Yingshan formation in the central Tarim basin

DENG Xing-liang, ZHANG Qing-yu, LIANG Bin, DAN Yong, LI Jing-rui, HAO Yan-zhen

2015, 34(2): 154-158. doi: 10.11932/karst20150208

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As part the central uplift of the Tarim basin, the Tazhong (central Tarim) II area is a low swell of the middle section of this uplift belt. In this area, before sedimentation of the Lianglitage formation, the strata of the Tumuxiuke, Yijianfang and Yingshan formations had experienced erosion of different degrees, leading to destruction of the original landforms. To delineate the karst paleomorphology of the top Yingshan formation is of great importance for modeling of karst reservoirs and forecasting favorable blocks in exploration. This work compares methods for paleogeomorphology reconstruction. The impression method can well describe micro morphology, but its resulting regional tectonic trends do not accord with the real ones. While the residual thickness and residual thickness trend surface method is able to build the palaeostructure at that time, but cannot depict the micro morphology. To solve this problem, this study proposes a combination approach of “residual thickness of trend surface and impression residuals” to recover the ancient karst landform. This new method not only facilitates the paleogeomorphology restoration of the Tazhong area, but also helps computer modeling. The research suggests that the Ordovician Yingshan formation of the Tazhong II area can be divided into three kinds of second-order geomorphic units， karst platform, karst basin, karst gentle slope, and gives the index system for subdivision of these landform units.

Characteristics of oxygen and carbon isotopes of karst fissure-cave fillings in the Yingshan formation, TazhongⅡarea，Tarim basin and their implications for environment

ZHANG Zheng-hong, DAN Yong, LIANG Bin, ZHANG Qing-yu, LI Jing-rui, HAO Yan-zhen

2015, 34(2): 159-164. doi: 10.11932/karst20150209

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This work is based on analysis of logging curves, core observations and thin section identification to fissure-cavity filings from Yingshan formation of Ordovician in the Tazhong II area, Tarim basin. The results show that the fillings are of high GR values in logging curves and their lithology is dominated by calcareous-argillaceous material and breccias. Comparison of oxygen and carbon isotopes with bedrock indicates that the calcareous-argillaceous filling contains 0.6‰ to 1.04‰ ofδ13C and -6.8‰ to -5.5‰ of δ18O, of which theδ13C value is obviously more positive. However，theδ13C andδ18O values of small breccia fillings are -0.13‰ and -6.29‰, respectively, consistent with that of bedrock. Both the fluid nature and ancient hydrological setting were variable when the fillings formed, resulting in different oxygen and carbon isotope values. Thus such values can be used to estimate fluid properties and ancient hydrological environment. Based on previous studies and the results of this test, we consider that the calcareous mudstone in caves was filled in a marine environment during the Lianglitage period and breccia fillings might be formed by collapsed or broken bedrock around caves. This recognition provides evidence for the study of filling mechanism in ancient karst fissure-cave reservoirs and establishment of paleokarst models.

Development model of compound buried-hill reservoirs in the Yingmai 32area of Tabei and its significance for exploration

LUO Ri-sheng, HUANG La-mei, CUI De-yu, LUO Xin-sheng, ZHU Yong-feng

2015, 34(2): 165-170. doi: 10.11932/karst20150210

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A special type of buried-hill reservoirs, which is compounded by both carbonates and sandstones, has been discovered in the Yingmai 32 area of Tabei (North Tarim). This paper describes part of these reservoirs and analyzes structures and sedimentary history of the Yingmai 32 area. We suggest that the key reason for the generation of such reservoirs is that multiple-episode truncations and overlaps have happened along the unconformity surface of basement rocks. The two enormous unconformities that developed during the Middle to the Late Caledonian period and Hercynian to Indo-China period set up the foundation for the building-up of these compound reservoirs. The reservoirs could be divided into two types: truncation type and overlap type. The truncation type can be further divided into three different models: overlap, pinch-out and graben models, while the overlap type includes three sub-models: overlay, pinch-out and gully models. Such compound buried-hill reservoirs are common in Tabei. Thus we should make more efforts to describe the top surface of all connected reservoirs instead of carbonates alone, which would significantly contribute to expansion of hydrocarbon exploration.

Characteristics of karst reservoirs in the Ordovician buried hills of the Halahatang area，northern Tarim basin

ZHAO Kuan-zhi, DAN Yong, ZHENG Duo-ming, LIANG Bin, ZHANG Qing-yu, LI Jing-rui

2015, 34(2): 171-178. doi: 10.11932/karst20150211

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Crack-cavity type karst reservoirs, which lie in the Ordovician buried hills, are the primary production horizons of the Halahatang oil field northern Tarim basin. Based on karst geology background and tectonic evolution of this area，using integrated data of drilling-logging wells，thin slices and seismic surveys, this work analyzes the characteristics, spatial distribution, and controlling factors of the karst reservoirs in this area. The results show that these reservoirs are largely present in the Middle Ordovician Yijianfang formation and the Lower-Middle Ordovician Yingshan formation. In vertical direction, there are two sets of reservoirs in verti in the buried hills, which are the upper superficial dissolution belt and lower runoff dissolution belt. The superficial belt contains cavity type and crack-cavity type reservoirs, which are controlled by karstification at the ends of the deposition of both the Yijianfang and Sangtamu formations. The runoff type of reservoirs are of cavity and crack-cavity types, which are dominated by karst channel systems, determined by multiple episodes of karstification including the end Lianglitage period and end of the Sangtamu formation sedimentation. Many factors, such as the layers of karst, episodes of karstification, ancient landforms, ancient drainages and faults, jointly controlled the distribution of karst reservoirs, resulting in complicated crack-cavity systems in this area.

Ancient hydrological conditions of the Ordovician transformation zones in the Halahatang area, northern Tarim

ZHENG Duo-ming, ZHANG Qing-yu, ZHAO Kuan-zhi, LIANG Bin, DAN Yong, LI Jing-rui

2015, 34(2): 179-186. doi: 10.11932/karst20150212

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From north to south, the Halahatang area of northern Tarim can be divided buried hill in karst, interbed karst bedding reform, interbed karst platform-margin overlap, and karst slope zones. Among these, the inter-bed karst-bedding reform zone is the transition area between the buried hill karst and bedding karst zones. This paper presents a detailed analysis on the ancient karst hydrological conditions for sediment discontinuity in the Pre-Silurian and Lianglitage formation karst period. The results suggest that the surface drainages are characterized overall by runoff from north to south and deeply incised valleys that decided the depth of the local discharge datum. There are various kinds of underground rivers, which are of flow in and flow out types as pipeline systems, mostly in single inflows and outflows. On seismic reflection profiles, these rivers can be recognized by continuous or intermittent beaded strong reflections, of which the karst subsurface river of the Lianglitage formation is particularly obvious. Most of beheaded rivers of the Pre-Silurian have hidden outlets. In the vicinity of these underground rivers, there exist big fissure-cavity bodies which are the important targets in current exploration. Thus accurate reconstruction and description of the hydrology of these ancient karst drainages would be help to search for favorable reservoirs of hydrocarbon.

Characteristics and identification of dolomite intercalation in the Yingmai buried-hill area, northern Tarim uplift

HUANG La-mei, LUO Ri-sheng, HAN Jie, ZHUANG Xu, CUI De-yu

2015, 34(2): 187-194. doi: 10.11932/karst20150213

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The crack-cave type dominates dolomite reservoirs in the Yingmai buried-hill area, which include dissolved holes, karst caves and karst cracks, as well as local big unfilled caves as storage space. The bottom water massive reservoirs in dolomite buried hills are controlled by dolomite intercalation with special physical properties. Local residual oil enrichment areas are the main object in the late exploitation. Basing on analyses of cores, thin sections, physical properties and well logging data, this work made a description and identification of dolomite from Cambrian to lower Ordovician in the Penglaiba formation of the Yingmai buried-hill area. The results show that, the intercalation in this area can be classified into 3 categories, micritic dolomite intercalation, mud dolomite intercalation and powder dolomite intercalation. Vertically, dolomite intercalation mainly developed in the lower part of the shallow upward sequence in each meter scale cycles, and always spread as lens or bands of which the thickness is between 0.5 and 2.5 meters. In this area，the intercalation played the screen role to seepage and controlled the distribution of residual oil, and also affected the water breakthrough time and the rising rate in production.

Experiments on solubility of different acidizing fluids to Syrian limestone

GAO Xiang, JIANG Jian-fang, WU Chuan, LIU Guang-pu, LI Long, JIANG Rui

2015, 34(2): 195-200. doi: 10.11932/karst20150214

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Acidizing stimulation treatment always plays a very important role in enhancement of the production of oil and gas wells. Whether the characteristics of the chosen acid fluids used in the acidizing treatment meet the quality of formation determines success of the treatment. With development for more than half century, it has already evolved from conventional acids including normal hydrochloric acid and mud acid to retarded acids including multicomponent acid fluid, emulsified acid fluid, gelled acid fluid and surface cross-linked acid fluid. However, many of the unconventional oil and gas reservoirs are buried very deep, which leads to the reaction temperature between acid and formation rock becomes higher. This can fasten the reaction rate of acid and rock, decrease the effective distance of live acid, and lower the efficient acid fluids. The final result is the stimulation treatment cannot remove the damage of near well-bore, increase the production of oil and gas wells and reach the aim of deep-penetration. To solve the problems above, many researchers made character evaluation of only 1 to 2 acid fluids and the temperature in the experiments is too limited, which is not enough to many unconventional reservoirs. Besides, to retarded acids, exploring the reaction mechanism from the perspective of molecular is essential. Based on SY/T 6526-2002 of “Method of Testing the Rate of Dynamic Reaction between Hydrochloric Acid and Carbonate”,several experiments were conducted on the solubility of hydrochloric acid, organic acid (hydrochloric acid combined with acetic acid), gelled acid, emulsified acid and surface cross-linked acid to Syrian limestone powder by using acid - core reaction device under the conditions of high pressure and temperature in laboratory. The results show that，(1) The solubility of five acidizing fluids to limestone is above 90% in 2 hours. (2) The solubility of hydrochloric acid and organic acid to limestone is stronger than other three kinds of retarded acid. (3) Although the speed of dissolution of emulsified acid and surface cross-linked acid is slow, correspondingly low solubility under 95℃, due to destruction of stability of emulsified acid under the condition of higher temperature of 150℃, both the rate of dissolution and the solubility are highly enhanced. (4) In temporary condition, the inhibiting effect of “multiphase isolation” for H+ is stronger than high viscosity, and the more complex the linking between macromolecules is, the severer constraining effect for H+ will be. (5) The increase of temperature obviously speeds up the rate of dissolution, and has a great effect on the solubility of gelled acid, emulsified acid and surface cross-linked acid, but not at all for normal hydrochloric acid and organic acid. We obtained several different acidizing fluids’ reaction rates and solubility values at different times under different temperatures, which would be helpful for the optimization of acidizing fluid systems in oilfields.

2015 Vol. 34, No. 2

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