In the past three years, under the influence of international crude oil prices, the domestic oil and gas industry has been facing a huge cost pressure; the application effects of geology-engineering integration are quite different; some projects lagged behind schedule, and the results are not satisfactory. To solve these problems, four points are put forward after many practices and considerations:First, the implementation plan and objectives of geology-engineering integration should be made based on the premise of economy; Second, "major staged-challenging contradictions" in the study of oil and gas reservoirs should be identified based on effective data, to solve field problems efficiently and quickly; Third, multidisciplinary integration of "geology-engineering" should be achieved using data as a link; Fourth, data "platformization" should be gradually promoted in projects with geology-engineering integration to expand the application scope and period of geology-engineering integration. To develop and play the practical role of geology-engineering integration characterized by highly practical technology and management, it is necessary to abandon some traditional academic management or concepts, be creative and bold in science and practice, and make it play an important role in any stage of the development of complicated oil and gas reservoirs.

Dagang oilfield is a typical complex fault block oilfield. After over 50 years of exploration and development, it is facing the issues of "4 highs, 3 lows and 2 unbalances". Under the dual pressure of land requisition and environment protection, and the low oil price, how to realize economic exploration and development and maintain sustainable development is a great challenge. Based on reviewing the issues and challenges, centering on "five fields construction", an integrated geology and engineering model with Dagang oilfield characteristics has been established, that is production construction in project manner, synergistic team organization, platform research and design, modular field construction, and digitalized production management. To date, this model has worked well in production. In the "cluster well site" productivity construction of old oilfields, well trajectory optimization by integrated geology and engineering research, and coupled design of downhole and surface design have been adopted, realizing intensive well construction, simplified supportive work and factory-like operation. In the recovery enhancement practice by combining secondary recovery and tertiary recovery, key technologies, program design and production performance regulation have been studied systematically, working out a tertiary recovery series which can meet the needs of different reservoirs. The production practices show integrated geologic and engineering research is an effective way to realize sustainable development for old oilfields with complex underground and surface conditions under low oil price.

The Junggar Basin in Xinjiang is the important onshore oil and gas accumulation site in China and its tight oil and gas potential is enormous, but its development is faced with multiple challenges, such as complicated geological condition, high engineering difficulty and high cost. The concept of geology-engineering integration was applied to focus on researching the development of tight oil reservoirs in Mahu area so as to increase its development benefit. To cope with the challenges in the process of well drilling and completion, the geological cognition and engineering practice were combined closely by taking a series of measures, e.g. establishing fine geological model and rock mechanics model, optimizing drilling tools and drilling fluid systems, conducting geosteering drilling in which adjustment is conducted while drilling, and optimizing the stimulation strategy based on fracturing simulation and experimental results. It is indicated that tight oil and gas in Mahu area can be profitably developed by drilling horizontal wells and conducting stimulated reservoir volume (SRV). The drilling ratio of horizontal wells is vital to the productivity of oil and gas wells. The drilling ratio and drilling efficiency can be improved effectively by means of geosteering drilling under the guidance of fine 3D geological model. Multi-stage SRV strategy in the pattern of division and cutting is suitable for Mahu area and the fracturing parameters of high sand concentration, large fluid volume and high flow rate are adopted. Based on researches, the reservoir quality, drilling quality and completion quality of newly developed wells in Mahu area are improved significantly, the profitable development of tight oil reservoirs are preliminarily broken through, and large-scale development and productivity construction of this block has been launched recently.

Influenced by the complexity inside the faulted -vuggy carbonate bodies, the first target drill-in rate of the fractured-vuggy reservoir in the Tarim Basin is low, complex formation pressure and stress systems lead to difficult drilling operation and frequent incidents, and it is hard to optimize effective measures for well completion and increasing production capacity. These have delayed the oil and gas development process. Based on geomechanical research, the idea of geological-engineering integration is proposed which involves interdisciplinary cooperation, fine fault interpretation and faulted-vuggy body characterization, and drilling success rate can be increased by quantitative optimization from well location, drilling process to measures related to well completing and production capacity increasing in the West Yueman oilfield in the northern Tarim Basin. In the study, by focusing on the distribution of faulted-vugg bodies and principle stress azimuth, the orientation of natural fracture permeability and well stability, optimization methods have been established for well location and deviated trajectory, the distribution of formation pressure has been predicted using well-seismic data, and based on which the wellbore structure was optimized. In addition, four kinds of methods for well completion and increasing production capacity have been proposed based on near-wellbore stress distribution, wellbore orientation and reservoir distribution. Application of these methods in three wells including W22, W20, etc. provided high production, and made continuous exploration breakthrough in the West Yueman block, northern Tarim Basin. The study idea proposed in this paper provides references for exploration and development of other fractured-vuggy carbonate reservoirs.

In recent years, Jilin oilfield invests 9.5 billion yuan for the productivity construction of one million tons in the new areas, and the output-to-input ratio of conventaionl refracturing in old areas is less than 1.0, and profitable productivity construction and stable prodution becomre more and more difficult due to the dual effect of its basic geological characteristics (low permeability and low abundance) and low oil price. In order to deal with these challenges and realize low-cost efficient development in Jilin oilfield, the new connotation of geology-engineering integration with the techncial concept of "large fracturing" as the core was proposed, and then a series of technological research and field test were carried out in low permeability oilfields, e.g. Xinli oilfield. The new connotation of geology-engineering integration is embodied as follows. First, according to the engineering and technological requirements, the data of the block is acquired and recognized again, including stratified yield, hydroscopicity, pressure, fracure azimuth and the stress of reservoir and barrier, so that the project design will be more targeted. Second, according to the fracturing technology and construction requirements, the well structure and surface location of the wells are reoptimized and the number of drilling platforms are optimized so as to minimize the total productivity construction investment. Third, based on previous geological recognition and drilling optimization, a series of fracturing technologies with "turnaround fracturing, energized fracturing, plugging contorl fracturing and interference fracturing" as the main parts are developed. And fourth, a series of supporting technologies are innovated, including oil production, water injection, surface engineering and Internet of Things, to reduce the disposable investment and cut down the operation cost. This technological mode is applied to the productivity construction of new areas (e.g. No.3 platform in block Ⅲ) and the potential tapping of old areas (e.g. the middle area of block VI), and the application results are remarkable. Compared with the main area, No.3 platform is 40% higher in initial production, 57% higher in stable production, 8.2% higher in return rate and 16% lower in productivity construciton investment of one million tons. After fracturing is carried out in the middle of block VI, the single-well cumulative oil increment is over 400 t in the commissioning period of 16 months, its stimulation result is 4 times of the conventional fracturing result, and the output-to-input ratio is higher than 2.0. It is practically indicated that the integrated geology and enginnering mode with the engineering as the core is currently the effective way to solve the difficulty of profitable development in the low permeability oilfields whose geological situations are understood more definitely.

The tight sandstone gas reservoir in Kuqa foreland area is the principal natural gas productivity construction block in Tarim Oilfield, and its natural productivity is low. In order to realize beneficial development, it is necessary to carry out stimulation to increase the production. The reservoir is characterized by ultra-depth, high temperature and high pressure, high earth stress, developed natural fracture and strong heterogeneity. It is mainly faced with the challenges that the production increasing mechanism is not defined clearly, effective technologies are deficient, well conditions are severe, stimulation situations are complex and large-scale stimulation operation is risky in safety. To deal with these challenges, Tarim oilfield carries out a series of researches. First, it insists on geology-engineering integration, sets up a multi-disciplinary production increasing integration team and builds up the integrated working mode innovatively. Second, it coordinates domestic and foreign technical force by means of the open market cooperation mechanism. Third, by virtue of technological resource integration, the reservoir is further recognized and the production increasing mechanism is clarified. And accordingly the production increasing concept of fracture network stimulation aimed at activating natural fractures is determined, the technologies of fracture network acid fracturing and fracture network fracturing are developed innovatively, and the stimulation technology optimizing strategy based on the fracturing property of natural fracture is established. Fourth, based on the understandings of well condition and stimulation behaviors, high-pressure fracturing truck unit and large-bore completion string are prepared and two sets of weighted fracturing fluids and one dedicated acid corrosion inhibitor are developed to ensure the large-scale stimulation. The production increasing mode of geology-engineering integration is developed and improved continuously in practice. And the developed key technologies have been applied in 76 wells, whose single-well average production is increased by 3.28 times. The research results provide the technical support for the beneficial development of tight sandstone gas reservoir in Kuqa foreland area.

Fuling shale gas field is different from the shale gas zones in the North America in terms of surface and underground geological conditions. And the key to the economic and efficient development of shale gas in Fuling shale gas field is how to organize and conduct multi-well fracturing engineering design and field construction in the mountainous environment. The overall parameter design technology and operation mode of zipper fracturing based on the concept of geology-engineering integration was established in the pattern of efficient productivity construction according to the construction demand of Fuling national shale gas demonstration area. To increase the shale gas well productivity overall and satisfy the operational demand and characteristics of "well factory" in the mountain areas of Jiaoshiba block, the technological parameters were optimized from the aspects of prefrac key geological factor identification and analysis, areal-lateral-interval multiple level engineering parameter design, dynamic adjustment of field construction, etc, and then the overall parameter design technology of zipper fracturing with three-dimension cross fracture arrangement as the core was innovatively developed. And thus, geology-engineering integration and single well-well group batch construction are realized for the shale gas development in Jiaoshiba block. It was practically applied to over 4000 intervals in more 200 wells cumulatively. It plays a remarkable role in increasing the production rate of horizontal well group, improving the fracturing time efficiency overall and reducing the comprehensive cost. And it provides the powerful technical support for the fast and efficient productivity construction of 50×10⁸m³ in the first stage of Fuling shale gas field.

The shale gas reservoir in Weiyuan block is characterized by complex surface condition, deep buried depth, complex structure, strong heterogeneity and difficult fracturing stimulation. To deal with these difficulties, a series of technologies and measures are adopted. First, the development concept of "integration, industrialization and efficiency" is followed firmly, and the geology-engineering integration technology is adopted to confirm plane and vertical sweet spots and optimize the well design. Second, accurate geosteering is realized to increase the drilling rate of sweet spots greatly. Third, the quality of drilling engineering is improved so as to shorten the drilling cycle effectively and reduce the incidence of complex downhole conditions. Fourth, the fracturing process design is optimized to maximize the fracturing volume. And thus, the relatively perfect integration model of project management, research design, field research, geological drilling and geological fracturing which can be well used as the reference for the exploration and development of shale gas in the setting of complex marine is formed, the single well production is increased continuously, the single well cost is reduced steadily, and shale gas in Weiyuan block is developed effectively in the large scale. Next, it is necessary to practice and complete the geology-engineering integration technology continuously, deepen geological cognition and strengthen the support engineering technologies so as to realize the efficient development of shallow shale gas reservoirs above 3500 m and the profitable development of deep shale gas reservoirs in Weiyuan block.

Baode CBM field is located in the north of Hedong Coal field in the northern section of west Shanxi flexure zone, eastern margin of the Ordos Basin and its CBM resources are abundant. The CBM reservoirs in Baode Block are geologically characterized by shallow burial depth, low gas content, frangibility, collapsibility, low mechanical strength, low porosity, extra low permeability and underpressure, so its exploration and development are faced with a series of technological problems, including geological evaluation, well drilling and completion, reservoir stimulation, gas production engineering and surface gathering. To solve these problems, PetroChina Coalbed Methane Co., Ltd. reviewed previous exploration achievements systematically, and then analyzed comprehensively the geological and reservoir characteristics of middle and low rank CBM in the study area based on existing data of various coal fields, e.g. borehole, seismic, drilling, logging, well test and sample assay. It researched the evaluation technology of fine CBM area selection and developed a series of exploration and development technologies suitable for middle and low rank CBM. It also insisted on geology-engineering integration research to break through the bottleneck of CBM exploration and development technologies. Besides, it completed and optimized continuously the technological solutions from the aspects of geophysical exploration, well drilling, fracturing, drainage gas recovery and surface engineering. Thus, the CBM in Baode block is developed efficiently and China's largest middle and low rank CBM field is built up.

The exploration-production integration is one of the contents of cost reduction, efficiency increase and petroleum system management reform. The exploration shall make full use of limited funds to efficiently provide sufficient effective reserves for development. Therefore, it is necessary to reverse the phenomenon that more and more economic recoverable reserves are turned out be practically unrecoverable reserves. It is recommended to investigate the actual recoverability of existing remaining economic recoverable reserves and classify those reserves based on different areas, and the method shall be implemented when the reserves is submitted in the future. It is necessary to recognize the importance of potential tapping for reserves and production increasing in the mature oil fields from the strategic perspective of sustainable development, and extend the exploration to the development. It is suggested to check the submitted reserves based on abundant new cognitions obtained from previous development and exploit new series of strata, new types and new blocks constantly. These are important measures to increase the reserves efficiently and deal with low oil price.

The exploration and development of deepwater oilfield faces challenges such as insufficient experience, complex deep-water environment and underground factor, higher single-well investment cost, and difficult cost recovery, so that simply using the exploration-development integration mode for onshore and shallow water fields is difficult to meet the requirement of deep-water oilfield. The concept of geology-engineering integration is proposed, incorporating subsurface uncertainties, time and cost elements, which forms a reservoir evaluation and decision-making system, and based on which the evaluation mode, decision-making method and supporting drilling and completion technology have been researched and developed for deepwater oilfields. Evaluation practice in the deepwater pre-salt reservoirs in Brazil shows that the divisional evaluation mode called "one body and two axes" and information-value-oriented decision-making method would be favorable to promote the process of integrated exploration and development, shorten the evaluation period, maximize the evaluation benefit and make scientific decisions for deepwater oilfield. The application of pre-salt drilling and completion technology has greatly improved the drilling efficiency and reduced the drilling cost while accumulating experience for development wells. The successful application of the geology-engineering integration has proved it effective in deepwater oilfield and reservoir evaluation.

Tight glutenite reservoirs in Block Madong 2 at the eastern slope of the Mahu sag in the Junggar Basin are buried deeply, poor in physical properties, and very sensitive to water and pressure; and the glutenite is hard to grade, strongly heterogeneous and brittle, so that it is difficult to get economic exploitation. With experiences from adjacent regions, and integrating geologic cognitions with engineering techniques, the engineering design of the first horizontal evaluation well (Madong 1) in this block was optimized, and the advanced technology was introduced to guarantee application effect. Specifically, many core experiments and fine well logging interpretation were conducted to identify the lithologies and physical properties of the glutenites; fine seismic acquisition, processing and interpretation were carried out and the method of classifying glutenite reservoirs was established to optimize target layers and well trajectories; advanced geosteering tools and real-time model-updating technique were used to increase drill-in rate and drilling efficiency; and well test and numerical stimulation were performed to study factors affecting post-fracturing production of glutenite reservoirs and optimize engineering techniques. Base on multidisciplinary cooperation, Well Madong 1 obtained average oil production of 53.9 t/d through a 3-mm choke at stable water cut. Such production increase is much higher than a vertical well in the block.

Aiming at two core technologies (fracturing pressure analysis and numerical simulation) for post-fracturing evaluation, the technical process and potential of production increase of hydraulic fracturing were evaluated. After hydraulic fracturing operation, fracture parameters such as length, width and conductivity can be obtained by fitting net fracturing pressure; 3D fracture pattern can be described in details by 3D software simulation; and effective fracture length and fracture conductivity etc. can be obtained by numerical simulation of production history to further evaluate fracturing quality and effectiveness in a scientific and reasonable way, and therefore evaluate the technical process of hydraulic fracturing. The potential of production increase can be evaluated by production performance analysis after hydraulic fracturing. As the fluids in fractured tight sandstone reside in two interconnected systems (the matrix provides main reservoir space, and the fractures provide major flowing channels), based on the studies of geology-engineering integration, and using imaging logging data to characterize fractures, the method for calculating fracture porosity, facture permeability and shape factor of natural fracture systems is proposed; and by integrating matrix, natural fractures, artificial fractures, fluid/rock properties and production history, a dual-medium model is established which can simulate real production history after reasonable adjustment of some uncertain parameters in the model, so as to evaluate hydraulic fracturing effectiveness. This method is useful for fracturing evaluation, post-fracturing production prediction and optimization of fracturing stimulation plan. It can provide strong support for design and implementation of fracturing stimulation in exploration areas, new wells or new production zones.