The Study On Technical And Economic Evaluation Of Tight Oil Resources Development

Driven by high oil prices and technological progress over the past years,development of unconventional oil and gas resources enter into fast-growing channel.With tight oil’s scale benefit development of the United States gradually affecting the world’s energy supply and demand pattern and geopolitics;it has become the focus of the world’s unconventional oil and gas resources exploration and development.China’s unconventional oil and gas resources are abundant and the development potential is relatively large.Gradual development of unconventional oil and gas resources has become an important strategic decision to alleviate the contradiction between oil and gas supply and demand.With continuous breakthrough of tight oil’s exploration and development in the United States,more mature tight oil producing areas are gradually built.China has also accelerated the research progress of tight oil.When developing the tight oil resources,the technical and economic evaluation is also essential in addition to geological and reservoir evaluation.Compared with conventional oil and gas resources,the cost of developing tight oil resources is relatively high,and drilling engineering technology is more complicated than conventional oil and gas,and the whole production process decreases quickly,so the final production is not easy to predict accurately.These characteristics increase the economic risk of developing tight oil resources.So it is even more difficult to make economic decisions.Especially under low oil prices,new requirements for the economic evaluation of tight oil development are put forward.With the development of tight oil and gas resources in China,the establishment of technical and economic evaluation methods suitable for tight oil and gas resources has become one of the urgent problems that oil and gas development enterprises are facing.This will have great practical significance for the development of unconventional oil and gas resources industry in China.Therefore,based on the deep research on the present situation of tight oil development at home and abroad,key technology of tight oil development,and economic benefit of tight oil development under low oil prices,the seepage characteristics and production capacity models of tight oil are studied,and the technical and economic evaluation methods as well as the comprehensive evaluation model of the development of tight oil are discussed in this dissertation.The main body of the dissertation is divided into three parts.In the first part,full life cycle capacity prediction model for the fracturing horizontal well is tried to built based on the complex reservoir seepage model under tight oil’s " long horizontal well section and volume fracturing" development model,which provides practical tools for capacity forecasting for tight oil’s development.The second part is based on the economic evaluation theory of resource development projects and the technical characteristics and input-output rules of tight oil development projects,combined with actual situation of domestic tight oil development projects,the economic evaluation model for tight oil development projects is established which provides theoretical support for investment decision of China’s tight oil development.In the third part,this dissertation studies the comprehensive evaluation method,system and process from multiple angles to evaluate the benefits of tight oil development projects which can be an effective complement to the conventional cash flow method.Part One: Analysis on full life cycle capacity prediction model for the fractured horizontal well in tight oil reservoirs and the sensitivity factors.As an important input parameter for the technical and economic evaluation of tight oil development,the production of tight oil wells is the ultimate goal of long-term development of oil and gas field enterprises.Especially under the low oil prices,production evaluation should be included in the economic evaluation.Based on the differences in the technical level between tight oil and conventional oil resources and the problems in the production capacity prediction method,the seepage mechanism and the production capacity model of the tight oil were studied.Firstly,the nonlinear seepage mechanism of tight reservoir is studied.Under volume hydraulic fracturing,there are several different kinds of flow medium with different scales which have different flow rules and seepage mechanism.The research has shown that there are obvious nonlinear seepage mechanisms in tight oil reservoirs;some non-Darcy factors such as the threshold pressure gradient and pressure sensitive effect greatly influence the production capacity.Secondly,based on the nonlinear seepage mechanism of multiple medium with multi-scale in tight oil reservoirs,to be consistent with the actual dynamic production characteristics,the full life cycle capacity prediction models of fractured horizontal well in tight oil reservoirs are established with fully consideration of the impact of non-Darcy factors such as the threshold pressure gradient and pressure sensitive effect on the production capacity.Finally,the established model is applied in the practical reservoirs to predict the productivity of fractured horizontal wells of tight oil reservoirs,to obtain reservoir parameters by history matching,to optimize parameters of the horizontal well and fracturing scale,and conduct sensitivity analysis of the main factors of capacity.The results of analysis play a guiding role in the demonstration of reservoir engineering.Part Two: Research on technology of technical and economic evaluation of the tight oil development.Based on the discounted cash flow method,the economic evaluation model of tight oil development project is established.Based on sensitivity analysis method in uncertainty analysis,the boundary assessment method is constructed by the critical analysis which describes the investment critical point of tight oil development project with economic and technical parameters.Economic parameters include net present value,internal rate of return and investment recovery period,etc.And technical indicators include economic limit production,horizontal section length and artificial fracturing fracture series.In the case section,analysis of investment,cost,benefit and economic limit are carried out for the development of typical tight oil blocks in Changqing,Xinjiang and Sichuan.And a detailed sensitivity analysis is performed for the horizontal segment length and fracturing series in technical specifications.It is concluded that under the cost control,it is necessary to study reasonable horizontal section length and fracturing range of the fractured horizontal fractures from economic benefit point of view,and find out the best match point of single well production,the investment and the benefit under technical premise and actual complex geological conditions,so as to design the horizontal well development scheme from the point of view of economic efficiency and not only capacity maximization.Secondly,the overall economic evaluation of the pilot scheme for the development of tight oil reservoir of Jurassic system in the central Sichuan basin is carried out including the deployment for pilot scheme,investment estimation and economic evaluation of the pilot scheme.A total of six sets of implementation programs and a set of preferably well program are designed.Based on the above-mentioned whole life cycle capacity prediction model for the fracturing horizontal well,combined with numerical simulation,analogy method and empirical formula method to comprehensively determine the initial production capacity and cumulative oil production of tight oil horizontal wells.Based on the capacity prediction model and the optimization design method,the horizontal section length and fracturing parameters are optimized.Combined with calculation results of numerical simulation,analogy and other methods,the optimal range of horizontal well length and fracturing parameters is determined synthetically.The determing of the final value of these parameters will also take into account the current status of the process technology and investment costs constraint.Based on the financial analysis of the six sets of implementation programs and a set of preferably well schemes,sensitivity analysis of the selected scheme about NPV and IRR are carried out as well as critical analysis of oil prices,production,investment and cost.The anti-risk strength of these factors is analyzed.Scenario analysis is conducted for schemes including investment and tax scenario analysis to examine the economic benefits of each scheme under various scenarios.Part Three: Study on the comprehensive evaluation of tight oil development.Tight oil development enterprises are facing how to achieve efficiency development under the low oil prices,how to develop a scientific and comprehensive evaluation system based on the long-term development of enterprises to measure the comprehensive benefits which is the focus of investment decision-makers.This dissertation proposes a integrated evaluation method to evaluate project programs more comprehensive and objective.The establishment of comprehensive evaluation model includes four steps: construction of evaluation index system,determination of weights,standardization of indicators and calculation of comprehensive evaluation indexes.Tight oil development project is a complex system involving many fields such as economy,society,resources,environment,science and technology and management.The comprehensive evaluation index system can adopt tree structure to provide comprehensive evaluation of benefits about economic,social,resources,environmental,technology and management aspects from the perspective of sustainable development.The comprehensive evaluation model mainly adopts the analytic hierarchy process to construct weights of each level indexes.The construction process of weights needs to be closely integrated with the actual situation,and give full consideration to the opinions of the experts in the fields of economy,society and oil and gas development.Based on the comprehensive evaluation model,weights of tight oil development project evaluation indexes are determined according to existing development plans of tight oil blocks combined with the actual field data.The comprehensive evaluation and analysis is carried out for a tight oil development block in Changqing oilfield in order to reflect various aspects of the project in a comprehensive,clear and brief manner which provides a basis for the decision-making of enterprises.This dissertation makes a deep research on the combination of theoretical analysis and application examples for the technical and economic evaluation of the development of tight oil resources in order to provide systematic economic evaluation methods and processes for the oil and gas development enterprises.The main innovations are as follows.(1)A full life cycle capacity prediction model for tight oil development is established.Aiming at the production characteristics of fractured horizontal well and the different flow medium and seepage mechanism in the initial,transitional and later stages of production,the corresponding production capacity prediction models are established,and finally the life cycle capacity prediction model of fractured horizontal well in tight oil reservoirs is formed.(2)The evaluation index and parameters of the tight oil development project are established.The economic evaluation model and the technical boundary index evaluation model of the tight oil development project are established.Meanwhile,methods and steps of sensitivity analysis,critical analysis and scenario analysis are given.(3)The comprehensive evaluation index system of the tight oil development project including economy,society,resources and environment is constructed,and the comprehensive evaluation method is given.Tight oil development project is a complex system involving economic,social,resource,environment,science and technology and management.Carrying out comprehensive evaluation in addition to economic benefits about these areas from the perspective of sustainable development can reflect all aspects of the project more comprehensively and clearly.The comprehensive evaluation results can be used as effective supplement to the discounted cash flow method.The purpose is to provide a more comprehensive investment decision reference for the enterprise managers in the development of tight oil resources,and evidence for the relevant industrial policies.China’s development of tight oil resources is still in start stage overally.In addition to the evaluation of geological and reservoir for tight oil resources,technical and economic evaluation is needed also.Considering research results of economic evaluation for tight oil resources development are still few at present,this dissertation conducted a groundbreaking study about the seepage mechanism and production forecast of tight oil reservoirs,as well as the technical and economic evaluation technology,methods and systematic process of tight oil development projects.It provides decision-making reference for the oil and gas industry and enterprises,and theoretical basis for the country’s industrial policy as well.