| Lacustrine argillaceous dolomite reservoir have been explored in the Ⅲ-5 Member of Shahejie Formation, Tanggu District, Bohai Bay Basin, China. Accompanied by faulting activities frequently, the studied area have been transformed into complex fault blocks, and this reservoir have abundant secondary porosity and fracture. In recent years.the deep and unconventional oil reservoir is being explored throughout our country. Take the studied area for example, its estimating oil reserves has already been reached the level of small oil fields. Lacustrine and marine carbonatite reservoir have a widely difference in many aspects,such as the mineral compositon, sedimentary and reservoir characteristics, so we must analysis applicability and reliability of the principle and method in the study of all aspects.The reservoir have complex mineral compositon and fracture characteristics. The oil-water distribution and the controlling factors of petroleum accumulation have been unknown else. This thesis is based on core, logging data, assaying data, formation test and production information to finding the favorable target area. According to reservoir quality and oil-bearing possibility, this thesis analysis the main features and control factors of two main level in reservoir. This thesis is divided into six parts in content, such as regional tectonic evolution, fracture development characteristics and logging evaluation, cause and main controlling factors of fractures, physical property and oil saturation evaluation, establishing three dimensional constraint body of fracture control factors, reservoir fracture modeling.Regional tectonic evolution. The reasearch is based on the analysis of seismic section explainnation of tanggu uplift about the paleogene tectonic evolution. The evolution in the study area is divided into three episodes fault, one episode inversion of uplift and denudation of extensive exposure process. During the Ⅲ-5 Member of Shahejie Formation, under the union of Tangbei fault and F1 fault, it formed a horset in in the southeast, also a half-graben is formed in the northwest. During the Ⅳ-1 Member of Shahejie Formation, Tangbei fault continued to activite stronger, then decrease and stagnate. This period of development like flower structure and associated intensive secondary fractures of great significance to dolomite fracture development. Regional stress field in the period of I Member of Shahejie Formation is turn sinistral to right turning, but the deposition thickness was thin and record was incomplete. Dongying group sedimentary period, underlying formation in angular unconformity contact with, especially in the study area in the middle of seismic event cutting phenomenon is prominent, and directly contacted with I Member of Shahejie Formation, and it reflected rapid deposition--inversion of uplift--expostion and denudation. II Member of Shahejie Formation was missed in tanggu uplift. A great angle unconformity was appeared under the Dongying group base, the long-term exposure of the underlying strata denudation was because inversion uplift.Fracture development characteristics and logging evaluation. The study tries to explore the influence between fracture development characteristics and logging response, and support the essential correctness of logging evaluation model in mechanism. So the logging evaluation of fractures will be difficult, and core could help verifying the logging response features of fractures. Fracture development characteristics includes fracture density, dip angle, width, length and filling mineral. Fracture development characteristics is mainly controlled by sedimentation and geologic structure is AC、DEN、CAL、AC/DEN. AC/GR,which reflected on lithologic characteristic,such as mineral composition and layer thickness. The study about the mechanism of influence between fracture development characteristics and lithologic characteristics would have practical significance in the continental sedimentary facies. The features of logging response id devided to three classes in consideration of lithology and fracture patterns. Based on above study, we can screen sensitive logging curve of fractures, and build the model of electrofacies or evaluation model of fracture density. The correctness of logging evaluation model reaches 71.43%in the validation process which shows the reliability of evaluation model. The study shows that conventional and special logging have great difficulty in evaluating fracture in the complex reservoir conditions, but we can build the evalution model and improve its reliability on the strength of the study achievement about the relation in fracture development characteristics and logging response.Cause and main controlling factors of fractures. The research shows that the fractures is mainly the tectonic origin, the bedding fractures and dissolution fractures account for little, and the seepage ability decreases successively. According to the situation of analcime, asphaltene filling and karst development situation, there are four stages of fractures development including bedding fractures parallel to beddings, oblique fractures with 45 and 60 degrees, tensile fractures with 75 to 90 degrees, high angel fractures with 70 to 85 degrees. The structure, lithology, diagenesis and overpressure are the key control factors of fractures in lacustrine dolomite reservoir, which obviously influenced by cracks and stress field. The lithology:fracture development is accompany with the rise of dolomite, analcime content increasement; the structure:stress concentrated area, fault extension direction change, end caps, split and multiple faults, such as interlaced fault block area, fractures is developed; the diagenesis:fracture and dissolution are the key of diagenesis in the study area; The overpressure and the the fracture development is a positive correlation.Physical property and oil saturation evaluation. The study tries to focus on the suitability and reliability of general model on carbonate reservoir with the complex mineral compositon. Another, we tries to build the new model that it takes many factors into consideration. The new model aim to improve accuracy on physical property and oil saturation evaluation. The seepage channel of fracture-pore type reservoir involves both pore and fracture aspects. Therefore, the model of physical property and oil saturation should be builded individually in two aspects. The shale content is the basis data of the physical property and oil saturation evaluation, but we don’t build relationship between shale content and logging data. We get the shale content data included with the experimental analysis of mineral composition, the complex mineral compositin. we obtained the data through experimental analysis. We tried to explore the way which builded the model of fracture porosity with RM and RD. The fourth, determining the standard value of total/fracture porosity. Porosity which measured in lab is usually less than the actual porosity in the reservoir, because the fracture porosity is used to be ignored. The study shows that the accuracy of fracture areal porosity from XRMI is lower than the data from core.Building the model of oil saturation in matrix should take shale and fracture into consideration, so we achieved the best model from three evolving model. Eventually, we builded a set of useable model of physical property and oil saturation in the lacustrine argillaceous dolomite reservoir. The results showed, Ⅲ-5 Member of Shahejie Formation belonged to middle-low porosity, low permeability reservoir, with 7%～18% porosity and under lmD permeability. Lithology and oil content is relevant, while dolomite oil saturation relative to the highest (45.61%), followed by argillaceous dolomite (33.81%).Establishing three dimensional constraint body of fracture control factors. Fracture model is set up when the geological factors need to consider how to control the crack distribution as a constraint condition, not only through mathematical model for calculating fracture. Based on the formed geologic models in the generation periods of fracture, using Ansys, the finite software, to simulate palaeostress field and calculate the stress value in developmental stages. According to the results, strain energy density and fracture value was calculated, which fitted with core fracture density by mutiple regression correlation, comprehensive considering multiple parameters of fracture properties. The mathematical model of fracture development was then offered in order to predict the distribution of fracture and summarize its regularity in study area, which developed the special argillaceous dolomite reservoir. The fracture prediction model is different from single well core, logging data, which interwell unknown area is controlled by the geological statistics methods. It is a body data with a combination of factors about lithology, structure, which is calibrated through the core and logging, being used as the next step of reservoir fracture modeling constraints.Reservoir fracture modeling:based on material comprehensive processing, comprehensive research of sedimentary facies and lots of artificial drawing analysis, established structure, sedimentary facies, lithology, property, net/gross ratio and original oil saturation quantified model of Tanggu oilfield. Reserve calculation result show:the geological reserves simulation result is similar to the actual geological reserves, that indicates the geological model is reliable.The method of deterministic modeling and stochastic modeling interaction takes advantages of the two methods in sedimentary facies geological modeling and improve the sedimentary microfacies simulation accuracy.Lithologic modeling uses sequential indicator simulation with constraints of sedimentary microfacies and lithology trend surface. Porosity modeling is dual controlled by sedimentary microfacies and petrophysical facies. NTG model show that the physical property lower limit of the effective reservoir:porosity≥6.6%, permeablity≥12.5×10-3μm2.Using the input of fracture characteristic and constraint body of fracture control factors, we model fracture by DFN, which is coincident with geology understanding. Reserves calculation result shows that:tanggu district geological reserves of simulation results is almost equal to the actual geological reserves, the geological model is reliable.Based on the above study of six aspects, we analysed regional tectonic evolution, builded the logging evaluation model of fracture, physical property and oil saturation, analyzed the reservoir characteristics and controlling factors of fractures, establishing three dimensional constraint body of fracture control factors and model the reservoir fractures. This study showed he fractures mainly develop near the fault cross zone with 2 groups of NW and NE trending faults, and the above mentioned fracture development zone with high pressure called the sweet spots should be valued in oil-gas exploration. |
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