With the efforts for strengthening of geological study, development of exploration technology and creation of exploration management, new historic breakthroughs in oil and gas exploration have been made in Daqing exploration area since Daqing Oil Field Co. Ltd was founded in January 2000. The detailed exploration of lithologic oil reservoirs in the northern part of Songliao Basin leads to discovery of three targets each with the reserves of 5000×104t from Putaohua Formation. The additional oil in place is 3.1×108t. The additional proven reserves from Fuyang Formation is 4726×104t. Three substitute reserves zones are also found in the area. Xushen-1 well becomes an important discovery. Xuzhong Uplift of volcanic rock has a prospect for 1000×108t reserves. Major breakthrough is made in oil and gas exploration of Hailaer Basin. The reported proven reserves reach 2009×104t for the first time in the area while the proven and controlled reserves are 8229×104t. This article summarizes the main results, technological developments and work experience achieved in oil and gas exploration of Daqing Area in the past four years and explains the principles and orientation for exploration in the next stage.

Against the sedimentary background of fluvial and delta sedimentary systems in large depression-type lake basin, Songliao Basin certainly has the geological conditions for forming lithologic oil reservoirs in large areas. Vertically, the lifting and descending of datum level in various periods causes big difference in allowable space in the different stages. Therefore, there is a certain difference in the types of developed sandbodies. Meanwhile, the migration and accumulation conditions and distribution law of those lithologic oil reservoir of each assemblage are quite different owing to the difference in the buried depth of reservoirs and locations of hydrocarbon source rock. On the plane, the types of lithologic oil reservoirs are controlled by structural positions and maturity of sandstone. The lithologic oil reservoirs are formed mainly in the frontal facies zone outside the delta in the depression. The surrounding areas of the depression are the main locations for development of various subtle oil and gas reservoirs. Guided by the high-resolution sequence stratigraphy, the detailed geological study was made on Putaohua oil layer of Yaojia Formation in the northern part of Songliao Basin in the light of the actual conditions of the sandy-shale thin interbedded lithologic oil reservoir in the frontal facies zone of the delta. It is found that the oil and gas reservoirs are distributed in belts. Therefore, distribution of oil and gas reservoirs is divided into the belt for structural oil and gas reservoirs as well as the belt for structural-lithologic oil and gas reservoirs and lithologic oil and gas reservoirs, clarifying the orientation for exploration of subtle oil and gas reservoirs.

The deep layers of Songliao Basin include Jurassic Huoshiling Formation, Lower Cretaceous Shahezi Formation and fault-depression stratum of Yingcheng Formation, and Lower Cretaceous depression strata of Denglouku Formation and Mem.I+II of Quantou Formation. The fault controlling the depression is in the NNE and NW directions. The fault depression is distributed along Nenjiang fracture belt, Sunwu-Shuangliao fracture belt and Harbin-Siping fracture belt. The sedimentary time for Huoshiling-Shahezi Formation is the time for the fault depression to be extended at a large scale. At the end of sedimentation for Shahezi Formation, the large-scale reversal takes place, laying the foundation for reformation of strata in the fault depression period. Mudstone of lake facies and coal measure are the most important hydrocarbon source stratum series during the faulted depression period. The three sets of regional cap rock-Mem. II of Denglouku Formation, Mem.I and II of Quantou Formation and Mem.I of Qing shankou Formationseparate four sets of natural gas source-reservoir-caprock assemblages. Close to the palaeohigh of the source depression, the fracture belt controlling the depression and the palaeostructure in the fault depression are the favorable zone for natural gas accumulation

Hailaer Basin is the Mesozoic and Cenozoic basin located in the Paleozoic orogenic belt in Inner Mongolia-Daxing??anling area. This basin is composed of a number of relatively independent rift groups controlled by the fault of northeastern direction. The basin mainly has Lower Cretaceous strata, namely Xing??anling Group, Tongbomiao Formation, Nantun Formation, Damoguaihe Formation and Yimin Formation. Three sets of hydrocarbon source rock, with a large thickness and a high content of organic matter, developed in Tongbomiao Formation, Nantun Formation and Damoguaihe Formation. The types of reservoirs main include base rock weathering crust, sandstone, tuffaceous sandstone and conglomerate. The low stand fan caused by the low stand systems tracts and the fan delta sand body caused by the high stand systems tracts are the main oil and gas reservoirs. A number of source-reservoir-caprock assemblages developed under the regional cap rock of Damoguaihe Formation. Vertically, the oil and gas are abundant mainly above and below the unconformity surface, shaping the oil and gas reservoirs of four types-faulted block, fault-lithologic, lithologic and buried hill. Horizontally, the oil and gas are abundant mainly the source groove and the nearby fault belts. The twisted fault belts are the favorable zones for oil and gas accumulation

A number of sets of hydrocarbon source rock and multi-type reservoirs exist in the surrounding basins of Daqing Oilfield. The sedimentary cap rock and the conditions for hydrocarbon migration and accumulation are different owing to the different regional structural conditions of various basins. Based on the thickness of source rock, geochemical characteristics, reservoir characteristics and oil and gas reserves, the analysis is made on exploration potential in the key surrounding basins, such as Suibing Depression of Sanjiang Basin, Tangyuan Fault Depression and Fangzheng Fault Depression of Yi-Shu Graben, Mohe Basin, and Dayangshu Basin. The prediction is made on the favorable oil and gas zones of each basin and four main sets of formation series are located for exploration of the surrounding basins. Of those, the second formation series of Lower Cretaceous developed in Dayangshu, Tangyuan and Sanjiang as well as the fourth formation series of Tertiary developed in Tangyuan and Fangzheng are determined as the main targets for exploration. Therefore, Suibing Depression of Sanjiang Basin and Yi-Shu Graben are determined as the basins for strategic breakthroughs and Mohe Basin and Dayangshu Basin as the basins for strategic extension.

Daqing Oil Field has strengthened the efforts for study of high-resolution 3D seismic exploration technology in the recent three years and gradually developed its highresolution 3D seismic data acquisition, processing and interpretation technological families, which are suitable for lithological exploration of shallow and middle-depth layers and thin layers in the northern part of Songliao Basin, deep-layer natural gas exploration in the area and exploration of complicated faulted blocks in Hailaer Fault Depression. The quality of seismic data has been raised continually. In the northern part of Songliao Basin, the reflection video frequency is 70 ~ 80Hz for the seismic data T1, the reflection video frequency 60 ~ 70Hz for the seismic data T2, and the reflection video frequency is about 40Hz for the seismic data T5. In Hailaer Basin, the reflection video frequency is 55~60Hz for the seismic data T2 and the reflection video frequency about 45Hz for the seismic data T5. Daqing Oil Field conducted high-resolution 3D seismic survey for 4730.7 km2 between 2001 and 2003. Those technology have played a key role in boosting the reserves of lithologic oil reservoirs in the northern part of Songliao Basin, discovering the large-scale natural gas reservoir of deep-layer volcanic rock in the basin and high-yield faulted block oil reservoirs in Xing??anling in Hailaer Basin, and making breakthroughs in exploration of Budatecun buried hill oil reservoir and Tongbomiao lithologic oil reservoir.

The main reservoir for deep-layer natural gas exploration in the northern part of Songliao Basin is mainly volcanic rock of Yingcheng Formation, which is the reservoir medium with seams and pores containing tuff. Conventional drilling operation causes serious pollution of the reservoir. The high pressure differential at the well bottom and irregular borehole diameter affect discovery and appraisal of the gas layers through well-log and logging. Those issues directly impair natural gas discovery and confirmation. To solve the issues existing in the conventional drilling operation, seven items of research work have been completed in the recent years, such as study of wellbore structural optimization, application of low-density drilling fluid suitable for formation fluid properties and reservoir pressure coefficients, negative pressure value controlling technology at under-balance well bottom, development of the automatic parameters acquisition and analysis system for under-balance drilling, measurement tools for under-balance MWD for well bottom pressure and temperature, acquisition of formation pressure and determination of killing fluid density. A series of process technology has been developed for near-balance and under-balance drilling and completion. The near-balance drilling technology is used in drilling three wells including the deep Xushen-1 in the northern part of Songliao Basin while under-balance drilling technology is used in drilling the other eight wells in the area, such as Weishen-5. The high-yield commercial gas flow is obtained from those wells with the gas formations effectively protected. Those desirable exploration results have played a key role in discovery of the 1000×108m3 reserves of the deeplayer natural gas in Xujiaweizi region in the northern part of Songliao Basin

Daqing Oil Field has developed a number of new application technologies for geochemical well log for the purpose to solve the difficult issues concerning how to identify and assess the wellbore of the complicated oil, gas and water layers. A family of technology has been developed for identification and assessment of light oil layers, remaining oil and water layers and the oil, gas and water layers of volcanic rock. Such technology, which has played an important role in exploration of Daqing area, has been used to find a large number of wells with high-yield industrial oil and gas flow, such as well Bei-302 and Xishen-1. This article systematically briefs about the main results achieved from the study of integrated log technology for complicated oil, gas and water layers in Daqing area. The methods for data processing and appraisal are further improved and perfected in the study project.

Based on the in-depth analysis of bottlenecks in logging assessment of sandy-shale reservoirs and deep-layer volcanic rock reservoir in the northern part of Songliao Basin as well as the epimetamorphic rock dual-pore reservoirs in Hailaer, it is pointed out that the assessment is inaccurate that the sandy-shale reservoirs produce oil or water or produce oil and water at the same time. The main reason lies in assessment of water flowing property. The conception on free water, micro pore water and clay water is proposed in the light of the sandy-shale pore medium reservoir. Based on this conception, the saturation model of the water of three types is established. This model provides the new and effective means for assessment of oil and water flowing property, achieving good results in actual application. With the help of core scale logging method, the basic study is conducted to identify the lithologic character and quantitatively calculate the parameters of fractures. With adoption of conventional and imaging logging technologies, plates are formulated to identify the lithologic character of volcanic rock. The imaging and dual-lateral fracture width calculation formula is also revised. It is clarified that the imaging spectrum analysis technology is the most effective way for assessment of the physical properties of the epimetamorphic compact sandstone reservoir characterized in broken and network-shape fractures. The lithologic coefficient a and bond index m in the Archie model are also made available. The study has developed a complete set of methods to assess the dual-pore medium reservoir, including the methods and criteria for detailed division of volcanic rock reservoirs as well as identification of fluid properties. Those methods have achieved satisfactory results in actual production.

To meet the geological characteristics of volcanic rock in the northern part of Songliao Basin, fracturing risk prediction technology for volcanic rock reservoir, rapid interpretation technology on the fracturing site and controlling technology of the hydraulic fracture extension for volcanic rock reservoir are adopted to design optimization of fracturing volcanic rock reservoir. Based on the analysis and judgment of volcanic rock fracturing operation as well as the real-time on-site controlling methods, a series of technology has been developed in the light of the high temperature, long operational time and high pressure of volcanic rock fracturing, including the high-temperature resistant and shear resistant fracturing fluid system, downhole fracturing pipe string, surface fluid discharging and result-appraising system. The stimulation technology for deep-layer volcanic rock gas reservoirs in the northern part of Songliao Basin is preliminarily shaped at the present time.

The petroleum geological experiment technology of Daqing Oil Field is developed into six main analysis and testing families, 18 items of testing series and 108 items of analysis technology. Crude oil fingerprint chromatogram technology is used to test distribution of productivity for mixed producing formations, solving the bottleneck of fourlayer production. Inclusion micro Fourier infrared spectroscopy technology provides the new means for study of the oil and gas migration and accumulation periods. Creation of illite crystallinity inspecting technology can quantitatively determine rock metamorphic grades. Rock swelling rate inspecting technology helps identify the reasons for reservoir damage. The study of experiment technology for simulation of reservoir damage caused by drilling fluid plays an important role in protection and emancipation of reservoir. Inspection of oil saturation in core drilling with keep-up pressure can truthfully reflects distribution of fluids in the reservoir.

With the exploration tasks becoming more and more difficult and the exploration information swelling rapidly, the current exploration data management is inadequate to meet the demand for exploration production and study. It is necessary to establish the exploration information system of Daqing Oil Field. Based on the investigation both at home and abroad and with the advanced information management technology and experience borrowed, the principle for the exploration information system has been formulated in the light of the actual condition of Daqing Oil Field. A three-level information system structure of ??specialized databank, central major databank and project databank?? is preliminarily shaped at the oil field and gradually perfected in the practice. The targets have been identified to perfect the information system, namely one main databank of exploration center at the level of oil field, five project databanks and seven specialized databanks. Establishment of the three-level exploration information system will provide important guarantee for technological study and raise the exploration efficiency. Meanwhile, establishment of digital oil (gas) reservoirs will inevitably reduce the exploration risk and boost the exploration performance.

Daqing Oil Field started to carry out exploration project management from the 1980s. This practice has played an important role in oil and gas exploration process and achieved remarkable results. Facing the new situation in the new century, Daqing Oil Field has borrowed the extensive experience in exploration project management from the oil companies both at home and abroad and strived to perfect the oil and gas exploration management system and operational mechanism centering exploration projects. With the efforts to establish reasonable managerial relations, clarify the responsibilities of each department, and set up the management system in the form of archives, the oil field is now able to make decisions scientifically, design and organize exploration projects carefully and focus itself on the quality in management of its oil and gas exploration projects. Those efforts provide the reliable guarantee for continually making breakthroughs in the oil and gas exploration of the three major fields--medium-depth and shallow layer oil exploration and deep-layer natural gas exploration in Songliao Basin as well as oil and gas exploration of Hailaer fault depression basin

Management of oil reservoir assessment at Daqing Oil Field can be summarized as follows: perfect organizational structure, clear management principle, effective management system of oil reservoir assessment, reasonable work procedure of oil reservoir assessment, creative project management pattern, consolidated supervision on project operation, assurance of the progress and engineering quality for the oil reservoir assessment project, conception of exploration-development integration, and overall performance of exploration and development. Suggestions are proposed for management of oil reservoir assessment at the next stage: further perfection of management process for oil reservoir assessment, establishment of the mechanism for reasonable interaction between exploration and development, consolidation of information infrastructure integration, establishment of effective information network for oil reservoir assessment, study and design the competitive mechanism for projects and maximization of the investment performance for oil reservoir assessment.

To avoid the decision-making risk and boost exploration results, the exploration plan can be brought under scientific management in three areas. First of all, the scientific properties of the plan should be stressed on the basis of strengthening the study of target optimization. The resources assessment in the related fields should be boosted so as to formulate the exploration plan on the scientific basis. The basic study for the plan should be conducted at various levels to locate the exploration targets for the exploration plan. The study of economic assessment for oil and gas exploration should be strengthened to solve the economic feasibility of the exploration plan and optimization of the plan. Secondly, the exploration plan should be based on the reasonable process so as to increase the possibility to fulfill the exploration targets. The reasonable formulation process of the exploration plan can promote combination between exploration plan and production. Target optimization in the exploration plan can further boost the effectiveness in implementation of the exploration plan. Thirdly, the exploration plan should be based on optimization of investment structure in order to ensure a long-term development of exploration work. Optimization of the investment structure for the exploration plan should take into account both the near-term and long-term development of exploration work. Such efforts will not only fulfill the annual reserves task and raise the grade of reserves for a higher exploration performance but also set the targets for strategic unfolding, strategic breakthrough and strategic preparation at the next stage.