Hill Reservoir Research Articles

The Numerical Simulation of Buried Hill Fractured Reservoir by CO2 WAG with Overlap Alternative Horizontal Well Pattern

For the trends of global climate warming, it is great important to implement the Carbon capture and storage (CCS) technology. This paper describes the numerical simulation of CO2 displacement enhanced oil recovery (EOR) in M reservoir. The M reservoir is an extra-thick buried hill fractured reservoir, which use overlap alternative horizontal well pattern to produce. Considering the time-varying effects of fracture’s porosity and permeability parameters, combining the develop dynamic and the diversification of physical property parameters of fractured formation, use the dual porosity dual permeability model and the three-dimensional components simulator to simulate the develop process. By CO2 WAG orthogonal experiment design, can simulate and predict the development effect of fractured buried hill reservoir affected by factors such as: different production and injection well pattern, injection intensity, gas water slug ratio, alternating cycle and so on. The results show that in the process of CO2 WAG can significantly reduce the risk of gas breakthrough by overlap alternative horizontal well pattern, and reduce the negative impact by fracture properties, also can improve EOR and CO2 sequestration effectively. On this basis, this paper evaluates the suitability of WAG development methods to fractured buried hill reservoir with overlap alternative horizontal well pattern, also optimizes the reasonable development plan for M reservoir.

Reservoir evaluation and fracture chracterization of the metamorphic buried hill reservoir in Bohai Bay Basin

Abstract With core observation, thin slice identification and imaging logging data, reservoir evaluation and fracture characterization are studied in the Archaean metamorphic buried hill reservoir in the JZ25-1S field in the Bohai Bay Basin. The reservoir is divided into three zones vertically: weathered crust, semi-weathered crust and base rock, belonging to three reservoir types of fracture-pore pattern, pore-fracture pattern and micro fracture-compact pattern. The fracture effectiveness is estimated using crude oil inclusions testing technology, the direction of regional geostress, and full wave train acoustic logging data. It is concluded that the reservoir in the semi-weathered crust is most developed and the reservoir of pore-fracture pattern is the main oil producing layer. The main trend of fractures is nearly parallel to the main fault trend in the buried hill. The inclined fractures of late opening-mode parallel to the current direction of maximum geostress are the most effective fractures. At last, in combination of imaging logging interpretation with actual production, the qualitative and semiquantitative reservoir classification criteria are proposed and the buried hill reservoir is divided into three levels of I, II and III.

Parameters Optimization of Stereoscopic Horizontal Well Patterns by Using Numerical Reservoir Simulation

Well pattern is the most important affecting factor to the ultimate recovery for an oilfield development. Many researches are reported on areal well pattern, which is widely used in conventional reservoirs development such as low permeability reservoirs, heavy oil reservoirs, multi-layer sandstone reservoirs, etc. In this paper, according to the geological characteristics of fractured buried hill reservoir of Liaohe Oilfield, we firstly present the concept of stereoscopic well patterns and compare it with common areal water flooding. By using numerical reservoir simulation method, we design and optimize the parameters of 5-spot stereoscopic horizontal well patterns, including payzone thickness and horizontal well length under different anisotropic factors of fracture permeability. This can be successfully applied on the development of MM block fractured buried hill reservoir of Liaohe Oilfield.

Physical Simulation for Water Injection of Horizontal Wells in Naturally Fractured Buried- Hill Reservoirs

It is very complicated for the relationship between water injection and injection-production through horizontal well in a naturally fractured buried-hills reservoir. On the basis of simplifying and hypothesizing for the flowing equations of the dual medium, the mathematical model for fluid flowing in a reservoir is obtained, and 7 similarity principles is proposed also. To aim at simulating the practical development effect, with the direction of the similarity principle, the triaxial fluid physical models were formed. With this model, the physical simulations, such as different well deployment patterns for the horizontal wells, various well distance, various difference between injection and production, were all carried out, the oil-sweeping mechanics for the horizontal wells were analyzed. Thus, the optimum well deployment patterns, well distance, differential pressure between injection and production were all Fig. out, so that the research achievement can provide a technical foundation for the production with water-injection within horizontal wells in a naturally fractured buried-hill reservoir.

A new method of metamorphicrock buried hill fracture reservoir modeling

Metamorphicrock buried hill reservoir is a type of complex fracture reservoirs and hard to characterize. The paper proposes a new method for buried hill modeling, to establish double porosity model, including fracture and matrix. In matrix modeling process, metamorphic lithology theory is used to characterize the complicated distribution of lithology for phase modeling, and matrix model with porosity and permeability under the control of lithology phase condition is completed by random simulation modeling. The data of lithology come from well logging in buried hill reservoir. In fracture modeling, the feature of strong anisotropy of permeability in formation is considered and a new method of fracture modeling is applied to characterize the fracture system. Then the method is used in history matching of real reservoir simulation to test the reliability, and the result shows the model by new method are closer to real reservoir than model by common method.

Optimization Deployment for Well Patterns of three-Dimensional Injection-production in the Buried-Hill Reservoirs

The optimum deployment of stereoscopically injecting and producing well pattern is a key to the buried hill reservoir's development. in the given reservoir, the spacing allocation factor of injecting and producing well type, vertical correspondent relationship, flat orientation relationship, injecting and producing well spacing for the stereoscopically injecting and producing the well pattern between the vertical well-horizontal well, horizontal well-horizontal well is optimized. With numerical simulation and by optimizing the multi injecting and producing schemes, the optimized scheme of stereoscopically injection-production well pattern for the buried hill reservoir is confirmed.

Features of buried hill reservoirs in Hexiwu structural belt, Langgu Sag, Jizhong Depression

Abstract The buried hill reservoirs of Hexiwu structural belt in Langgu Sag, Bohaiwan Basin are comprehensively studied by core and outcrop observation. The reservoir lithology is dominantly carbonate rock, and the reservoir spaces include dissolved pores, dissolved cavities, cracks and bedrock micropores, forming pore-cavity type, crack type, crack-cavity type and combination pore-cavity-crack type reservoirs. Multiple-phase fossil karstification is an important factor during reservoir formation. The fossil karsts are developed in the weathering and leaching belt, submerged current belt, fracture belt and bedding direction along buried hill unconformities. The cracks formed by tectonic movement increase porosity, improve connection of pores and cavities and permeability. The reservoirs developed in different lithologies and tectonic positions have different physical properties: dolomite reservoir is better than carbonate reservoir, and reservoir not overlapped by Permo-Carboniferous stratum is better than that overlapped by Permo-Carboniferous stratum, and reservoir in the fault-developed area is better than that in the non-fault-developed area. The reservoirs are favorable areas for oil and gas exploration.

Karst developmemt of buried dolomite hill reservoir in Wumishan formation of Renqiu oilfield

Based on the statistics of the features, dropping and leaking of well drilling, and the geophysical & logging data, the developing regulation of karst of buried hill in Renqiu oilfield was systematically studied. The results show that the period of the karst development is mainly in Tertiary, with spatial inhomogeneity. The inhomogeneity is mainly controlled by the geological construction in the horizontal direction. There are 3∼4 level karst developing zones in the profile section, which are mainly controlled by the intermittent subsidence of the earth’s crust started from Tertiary. The forming time of the lower karst zones is earlier than that of the upper ones. The horizontal karst zones are cut off by the latter faults. At present, the chief potential areas of residual oil of Renqiu oilfield are in the weak karst developing zones.

Exploration theories and practices of buried-hill reservoirs: A case from Liaohe Depression

Abstract In recent years, various breakthroughs have been made in buried hill reservoir exploration in Liaohe Depression. Exploration targets have shifted from the Shallow-medium buried hill reservoirs with clearer reservoir-forming conditions to the low and inner buried hill reservoirs with deeper, hidden, and more complex features. Reservoir-forming conditions of low and inner buried hills were studied in aspects of basement tectonic activity, type of buried hills, lithology and reservoir characteristics, hydrocarbon generating system, and hydrocarbon conducting system. A practical classification method of inner buried hill reservoirs has been reestablished in accordance with the relationship between buried hills and hydrocarbon accumulations by studying reservoir characteristics of inner buried hill reservoirs with consideration of exploration practices. Such a classification method has widened the hydrocarbon searching scope in buried hills and built up a reservoir-forming pattern for the exploration targets inside buried hills with low amplitude, multiphase fractures, and multisource charging. Based on the theoretical studies and exploration practices of low and inner buried hill reservoirs, the 3P reserves reported for low and inner buried hill reservoirs reached 2.54 × 10 8 t and 1.76 × 10 8 t, respectively, from 2001 to 2006. The buried hill reservoirs have made significant contribution to increasing reserves and stabilizing production in Liaohe Oilfield.

Study of the Law about Water-Cut Variation for the Fractured Metamorphic Reservoir of Buried Hill with Bottom Water

Aiming at the complex flowing environment including the buried hill of Metamorphite, the active bottom water and the fracture at Budate Reservoir within Beir Depression of the Hailar Basin, combining the laboratory studies and based on analysis of its drive mechanism, field wells’ parameters were used to analyze the effects of different conditions of the fractured metamorphic reservoir with bottom water on its law of wa-ter-cut variation and the waterflooding efficiency. The results show that for the Budate buried hill reservoir with bottom water, the gravity should be taken into consideration to determine reasonable perforation ratio and production pressure difference. And because of the acid sensitivity of the buried hill reservoir, application of proper clay stabilizer will enhance the field oil recovery to a satisfactory extent.

Diet and Reproduction of the Gray Redhorse (Moxostoma congestum) in a Texas Hill Country Stream and Reservoir

ABSTRACT Reproduction and diet of gray redhorse (Moxostoma congestum) were examined in a Texas Hill Country stream and a central Texas reservoir from September 2004 through August 2005. Temporal patterns in gonadosomatic index and oocyte diameter relative frequency indicated that M. congestum spawns over two distinct periods during spring and likely spawns multiple clutches in each period. Moxostoma congestum is an opportunistic benthic invertivore, with mollusks being the predominant food item in summer and aquatic insects the primary food item in other seasons. Additionally, diets differed between stream and reservoir habitats and among seasons. Though habitat degradation is of concern for M. congestum, our data suggest that it has persisted in habitats disturbed by low-head dam and mainstem reservoir construction due in part to its opportunistic feeding strategy that allows it to adapt to lentic systems.

Fluid inclusions in reservoirs of Weixinan Sag, Beibuwan Basin

Abstract To make sure the petroleum migrating direction and pool-forming model in the Weixinan sag, 4 wells were chosen to do research on fluid inclusions and petrography. The petroleum inclusions have three types: type I occurs in early cracks of quartz debris grains or the overgrowths inside, type II in the margins or overgrowths of quartz grains, and type III in late cracks of quartz debris grains. According to PVTsim, Ptr and Ttr are modeled and calculated. The results are: type I is 97.9 °C and 19.13 MPa; type II 112.6 °C and 35.05 MPa; type III 157.4 °C and 47.52 MPa. Based on burial history, three fluid-charging events occurred about 33Ma, 26.5Ma and 7Ma ago, respectively. Migration directions and pool forming models are: Fluid type II migrated towards westnorth and northeast respectively to form structural and lithologic reservoirs; Fluid type II migrated to areas surrounding the sag and formed block faulted and buried hill reservoirs; Fluid type III migrated to slopes to form anticlinal reservoirs.

Accumulation process and model for the Ordovician buried hill reservoir in the western Lunnan area, the Tarim Basin

The Ordovician buried hill reservoir in the western Lunnan area, a type of dissolved fracture and cavernous reservoir, is mainly composed of heavy oil. The oil is the mixture sourcing from the Middle-Lower Cambrian and Middle-Lower Ordovician, with three stages of pool forming process: (1) the destruction and parallel migration/accumulation during the late Caledonian to early Hercynian; (2) the oil and gas accumulation during the late Hercynian characterized by adjustment upward along faults and parallel migration/accumulation; (3) the formation of heavy oil during the latest Hercynian. The Ordovician buried hill reservoir is affected by the diffusion of light oil and gas but had no hydrocarbon charging during the late Yanshan period to Himalayan period, but in this period, formed the association of heavy oil and dissolved gas cracked from crude oil with dry coefficient of 0.91–0.96. The study on accumulation process of the Ordovician buried hill reservoir has important implications for the exploration potential of early oil and gas accumulation in the cratonic area of the Tarim Basin.

Geophysical evaluation methods for buried hill reservoirs in the Jiyang superdepression of the Bohai Bay basin, eastern China

The Jiyang superdepression is one of the richest hydrocarbon accumulations in the Bohai Bay basin, eastern China. Comprehensive seismic methods have been used in buried hill exploration in Jiyang to describe these fractured reservoirs better. Accurate seismic stratigraphic demarcation and variable-velocity mapping were applied to reveal the inner structure of the buried hills and determine the nature of the structural traps more precisely. Based on the analysis of rock properties and the characteristics of well-developed buried hill reservoirs, we have successfully linked the geology and seismic response by applying seismic forward technology. Log-constrained inversion, absorption coefficient analysis and tectonic forward-inversion with FMI loggings were applied to analyse and evaluate the buried hill reservoirs and gave satisfying results. The reservoir prediction was successful, which confirmed that the comprehensive utilization of these methods can be helpful in the exploration of buried hill reservoirs.

Runoff and water erosion modelling using WEPP on a Mediterranean cultivated catchment

Soil erosion due to water is a major environmental problem in many parts of the world. Most of Mediterranean countries are concerned because of their specific climate and soils sensitivity, but also because of the recent intensification of human activities and agricultural practices. Accurate estimation of soil water erosion for various land-use and climate scenarios is so an important key to define sustainable management policies. In the last decades, several studies have been carried out to build models suitable for quantifying soil erosion. Among these models, the Water Erosion Prediction Project (WEPP, Flanagan, D.C., Nearing, M.A., 1995. USDA-Water Erosion Prediction Project: Hillslope profile and watershed model documentation. NSERL Report 10, USDA-ARS National Soil Erosion Research Laboratory, West Lafayette, IN, USA.) is a physically based, distributed-parameter model that has been developed and mainly validated in USA. Only few studies have investigated its applicability to environmental conditions that differs from those where the model was developed. The aim of this work is to test the efficiency of WEPP model to predict soil erosion at catchment scale in a Mediterranean semi-arid area. Continuous simulations have been conducted between 1995 and 2002 on an cultivated experimental catchment located upstream from a hill reservoir (Kamech catchment, 2.45 km 2, Cap Bon, Tunisia) where runoff and soil erosion measurements are available at the outlet. Comparison between predictions and measurements shows significant differences. Processes related to seasonal effects (as cracking soils) are pointed out as a weakness of WEPP model for Mediterranean conditions.

Application of forecasting structural cracks technique of 3DMove in Chengdao buried hill

3DMove software, based on the three-dimension structural model of geologic interpretation, can forecast reservoir cracks from the point of view of formation of the structural geology, and analyze the characteristics of the cracks. 3DMove software dominates in forecasting cracks. We forecast the developments and directions of the cracks in Chengbei buried hill with the application of forecasting technique in 3DMove software, and obtain the chart about strain distributing on top in buried hill and the chart about relative density and orientation and the chart about the analysis of crack unsealing. In Chengbei 30 buried hill zone, north-west and north-east and approximately east-west cracks in Cenozoic are very rich and the main directions in every fault block are different. Forecasting results that are also verified by those of drilling approximately accord with the data from well logging, the case of which shows that the technique has the better ability in forecasting cracks, and takes more effects on exploration and exploitation of crack reservoir beds in ancient buried hill reservoirs.

Analyse du ravinement de bassins versants à retenues collinaires sur sols à fortes dynamiques structurales (Tunisie)

La production et le transfert de sédiments de deux petits bassins versants inscrits dans des marnes et alimentant des retenues collinaires en Tunisie semi-aride ont été étudiés entre 1999 et 2003. Le risque de comblement des retenues est surtout lié au ravinement qui mobilise sur les versants dix à cinquante fois plus de terres que l'érosion aréolaire. L'incision des ravins est évaluée par la comparaison diachronique de levés topographiques. Des modèles numériques de terrain sont ensuite construits pour établir les bilans volumiques des terres érodées ou déposées dans le ravin. Le ravinement varie fortement selon les intensités des précipitations et le type d'occupation des sols des impluviums. Au cours des quatre années de l'étude, le ravinement a fourni entre 15 et 65 m3/ha/an de terre aux retenues.

The Fundamental Thermal Niche of Adult Landlocked Striped Bass

AbstractResearchers have described the temperatures selected by landlocked striped bass Morone saxatilis in different locales throughout the USA. However, seasonally low concentrations of dissolved oxygen (DO) in many systems prevented striped bass from using the cool waters (<22°C) they may have preferred. In Melton Hill Reservoir, a 92‐km‐long impoundment on the Clinch River in east Tennessee, 15 adult striped bass were tagged with temperature‐sensing radio tags and tracked for an average of 418 d in 1999–2000. Cold, hypolimnetic discharges from an upstream dam and heated discharge from a steam‐generating electric facility near the midpoint of this run‐of‐the‐river reservoir provided a broad range of temperatures in most seasons, and hypoxic habitats were uncommon even during stratification. The mean temperature occupied by striped bass varied seasonally (repeated‐measures analysis of variance, P < 0.0001) and was highest in summer (17.5°C), intermediate in spring and fall (15.4–16.9°C), and lowest in winter (13.0°C). The mean and modal temperatures occupied during the growing season (May–October 1999) were 17.5°C and 19.0°C, respectively; 30% of the observations were between 9°C and 15°C. These data indicate that the fundamental thermal niche of adult landlocked striped bass may be lower than literature estimates. These results also represent the first unbiased field estimates of the influence of season on the thermal ecology of adult striped bass. The thermal characteristics of habitats considered optimal in habitat suitability index models for adult landlocked striped bass (i.e., 18– 24°C) should be revised to include cooler waters.

Quantification of water exchange between a hill reservoir and groundwater using hydrological and isotopic modelling (El Gouazine, Tunisia)

Stable isotope compositions (18 O and 2 H), determined for underground and surface waters from the watershed of a hill reservoir and downstream from the reservoir, suggest that (i) the reservoir water, which is more or less evaporated, represents a mixture between surface waters (rainfall, runoff) and the upstream alluvial groundwater meteoric in origin; (ii) the downstream alluvial groundwater have a stable isotope composition of a previously infiltrated reservoir water. The 18 O isotope enrichment modelling of the mixed reservoir water shows that an input flux of 50 m3 day−1 is balanced by an output flux of 300 m3 day−1 when the reservoir water level is above 4.5 m, and by an output flux of 170 m3 day−1 when water levels are lower. The contri- bution of hill reservoirs to local groundwater movements must be considered in any regional scale hydrological investigations of areas that contain hill reservoirs.

Use of a geomorphological transfer function to model design floods in small hillside catchments in semiarid Tunisia

In the beginning of the 1990s, the Tunisian Ministry of Agriculture launched an ambitious program for constructing small hillside reservoirs in the northern and central region of the country. At present, more than 720 reservoirs have been created. They consist of small compacted earth dams supplied with a horizontal overflow weir. Due to lack of hydrological data and the area's extreme floods, however, it is very difficult to design the overflow weirs. Also, catchments are very sensitive to erosion and the reservoirs are rapidly silted up. Consequently, prediction of flood volumes for important rainfall events becomes crucial. Few hydrological observations, however, exist for the catchment areas. For this purpose a geomorphological model methodology is presented to predict shape and volume of hydrographs for important floods. This model is built around a production function that defines the net storm rainfall (portion of rainfall during a storm which reaches a stream channel as direct runoff) from the total rainfall (observed rainfall in the catchment) and a transfer function based on the most complete possible definition of the surface drainage system. Observed rainfall during 5-min time steps was used in the model. The model runoff generation is based on surface drainage characteristics which can be easily extracted from maps. The model was applied to two representative experimental catchments in central Tunisia. The conceptual rainfall-runoff model based on surface topography and drainage network was seen to reproduce observed runoff satisfactory. The calibrated model was used to estimate runoff from 5, 10, 20, and 50 year rainfall return periods regarding runoff volume, maximum runoff, as well as the general shape of the runoff hydrograph. Practical conclusions to design hill reservoirs and to extrapolate results using this model methodology for ungauged small catchments in semiarid Tunisia are made.