Faced with various challenges involved in older, deeper and more complicated oil and gas exploration targets, PetroChina Company Limited (“PetroChina”) vigorously implemented resource strategies and promoted geologic cognition and innovation and engineering technology research during the 12^th Five-Year Plan. New geologic cognitions were innovatively obtained, such as “four-palaeos” (i.e. paleorift, paleo-bioherm beach complex, paleo-trap, and paleo-uplift) controlling the formation of marine carbonate reservoirs, extensive formation of clastics lithologic reservoirs, high-efficient formation of ultra-deep reservoirs in “four-in-one”foreland thrust belts (namely the belts with folded source rock, ultra-deep effective reservoir, very thick gypsum-salt rock, and imbricate structure), and formation of unconventional oil/gas (e.g. shale gas and tight oil) reservoirs. A series of new engineering technologies were developed, including integrated wide-azimuth, broadband and high-density seismic acquisition, processing and interpretation technology, logging evaluation and fluid identification technology for complex reservoirs, safe and fast drilling technology for ultra-deep layers, and horizontal-well volume fracturing technology. During the 12^th Five-Year Plan, 15 large-scale oil and gas reserve zones were discovered, contributing to the performance with proved original oil in place (OOIP) over 6×10⁸t for 10 consecutive years and proved original gas in place (OGIP) over 4000×10⁸m³ for 9 consecutive years. It records the peak period with the longest duration and the highest total production in the history of PetroChina. During the 13^th Five-Year Plan, PetroChina will encounter new situations with changed external environment (e.g. low oil price, and launching of the latest versions of Production Safety Law and Environmental Protection Law) and many internal challenges (e.g. increasing complexity of targets and deterioration of resource quality) in exploration and development. The study indicates that, PetroChina is at the middle stage of exploration and its oil and gas technical innovation is in the period of speeding-up development. During the 13th Five-Year Plan, PetroChina will continue the resource strategies and persist in theoretical, technical and managerial innovation with marine carbonate rocks, tight gas and foreland thrust belts as the key natural gas exploration domains and clastics lithologic formations as the major oil exploration targets. In this way, PetroChina will devote to discover large-scale reserves with high efficiency and quality, in order to increase oil and gas reserves continuously at peak.

Basically, overseas hydrocarbon exploration is an international activity with limitations, risks, and economics. With the expansion of overseas business, CNPC has figured out and built a “trinity” management model for key overseas exploration projects after studying and benchmarking with management models of major international oil companies. Specifically, a management loop of “Research - Decision - Implementation - Adjustment - Reevaluation” has been established to organically integrate and provide whole-process monitoring on tasks in three aspects, i.e. technical support, headquarters decision and field implementation. By far, significant results have been obtained in Niger, Chad and other projects.

Practical oil and gas exploration in carbonate strata has proved that gypsum-salt rock plays an important role in hydrocarbon generation and accumulation. In this paper, the effect of gypsum-salt environment on hydrocarbon generation, reservoir-forming and hydrocarbon accumulation in carbonate strata was discussed through experiments. As for hydrocarbon generation, evaporative tide flat and lagoon are favorable sedimentary environments for the formation and preservation of source rocks. The modeling experiments on hydrocarbon generation potential of gypsum-salt rock-kerogen assemblage verify that gypsum-salt rock can promote hydrocarbon generation of source rocks remarkably. As for reservoir-forming, the dolomites coexisting with gypsum-salt rocks are the main reservoirs. The formation of evaporative tidal dolomite reservoirs is mainly controlled by supergene dissolution of atmospheric freshwater, and the quality of dolomite reservoirs can be improved effectively by burial dissolution. As for hydrocarbon accumulation, gypsum-salt rocks turn from brittle to plastic withi higher sealing capacity as the burial depth increases, which is favorable for the perservation of deep oil and gas. Physical modeling experiments on structural deformation reveal that, in the setting of compressional structures, discordant fold deformation occurs in presalt and subsalt layers and effective hidden traps are developed in deep layers, so large-scale oil and gas accumulaiton can be formed.

Based on measured data statistics, thin section analysis and comparative analysis, the genetic mechanism of high-quality glutenite reservoirs at the steep slope in northern Dongying sag was studied from the aspects of sedimentation, diagenesis and hydrocarbon generation. Two pore zones were found vertically at the steep slope in northern Dongying sag, at the buried depth of 1650-2450 m and 2950-3300 m respectively. The study shows that the pore zones are different in genetic mechanism. In the first pore zone (1650-2450 m), the reservoir space is composed of primary pores, which due to the significant control of sedimentation are developed in mid-fan glutenites with low shale content, better sorting degree and moderate grain size. In the second pore zone (2950-3300 m), the reservoir space is composed of secondary pores which were generated by the dissolution of carbonates, felspars and quartz, as the result of alternative dissolution between earlier alkaline fluids and later organic acids formed by hydrocarbon generation of source rocks. The carbonate cementation and hydrocarbon charging at the early stage inhibited the compaction and cementation, contributing to the preservation of pores.

The Zengmu Basin was formed gradually with the evolution of tectonic cycle in South China Sea. Since Cenozoic, it has undergone three major structural evolution stages, i.e., foreland fault depression in Eocene to Early Miocene, strike-slip transformation in Middle Miocene and regional subsidence in Late Miocene to present. The tectonic cycle in South China Sea has controlled the structural evolution of the Zengmu Basin and also the hydrocarbon accumulation conditions. Besides, it plays an important role in the generation and accumulation of hydrocarbons. Foreland fault depression is the major factor controlling the development of principal source rocks in this basin and the formation of sandstone reservoirs and structural traps at the southern flank of this basin. At the stage of foreland fault depression, delta coal source rocks and terrigenous marine source rocks were generated. At the stage of strike-slip transformation, carbonate reservoirs and carbonate formation were formed in central-northern area of this basin. The formation and distribution of regional caprocks in this basin have been dominated by the regional subsidence since Late Miocene.

Chang 4+5 oil reservoirs in Jiyuan area, the Ordos Basin, are characterized by low permeability, complicated oil-water relationship and greatly different oil-bearing potentials in and between layers, in addition to extensive development. Moreover, factors affecting oil and water distribution in the reservoirs need to be further ascertained. The analysis on the controlling factors of hydrocarbon accumulation shows that the large-scale extensive development of Chang 4+5 oil reservoirs are controlled by three factors. First, the widespread Chang 7 source rocks provide abundant resource base. Second, high porosity and high permeability reservoirs of delta front facies controlled by differential diagenesis act as the places for oil and gas accumulation. And third, a great number of fractures are important oil migration pathways. Locally, however, affected by source rock thickness, fracture development degree and reservoir heterogeneity, oil enrichment degrees are different. In this paper, a hydrocarbon accumulation pattern was innovatively proposed with Chang 7 Member as the oil source, oil migrating along fractures and permeable sandstones pathways, non-isokinetic multi-point charging vertically, and physical properties controlling heterogeneous reservoir formation. Based on this pattern, the reasons for the extensive development and different oil-bearing potentials of Chang 4+5 oil reservoirs are revealed geologically.

Deep tight gas in fault depression basins, as a kind of unconventional resources, is seldom studied. With tight glutenite gas in Shahezi Formation of Xujiaweizi fault depression, the Songliao Basin, as an example, its accumulation conditions were analyzed by using seismic, geochemistry and reservoir testing data from the aspects of structure, sediment, source rock, reservoir and reservoir-forming assemblage. In addition, resource potential of tight glutenite gas was predicted in accordance with hydrocarbon-generation kinetic theories. The results show that majority parts of the slope areas contain gentle structures, and there are few faults penetrating the Shahezi Formation and remaining in continuous activities in later stages, suggesting structural environment for hydrocarbon accumulation. The widely-distributed coal-bed source rocks with high gas-generation intensity provide excellent gas-generating conditions. Glutenites of fan delta and braided-river delta facies develop extensively, and reservoir formations are tight with secondary high-porosity and high-permeability belts in certain parts, providing preservation conditions. Source rocks and tight reservoirs are overlapped in close contact and near source rocks, presenting desirable assemblages. Drilling data indicate that this area contain gas generally. Breakthroughs have been achieved in horizontal and vertical wells. In accordance with hydrocarbon-generation kinetic theories, total resources of tight gas are estimated to be about 2395?0⁸ m³.

In the First Member of Qingshuihe Formation (Qing 1 Member) in Shinan area, the Junggar Basin, sandstones and glutenites are widely developed with complex diagenesis, which is an important factor affecting reservoir development. Based on analysis of thin sections, cast thin sections, scanning electron microscope (SEM) and X-ray diffraction (XRD), together with core observation, physical property data and log data, the diagenetic characteristics of the Qing 1 Member reservoirs were studied and the differences of diagenetic characteristics between sandstone and glutenite reservoirs were analyzed. It is shown that the Qing 1 Member reservoirs experienced three diagenesis, i.e., compaction, cementation and dissolution, and they were mainly at Period B of early diagenesis and locally at Period A of middle diagenesis. Compaction is the major factor leading to the physical property loss of Qing 1 Member sandstone reservoirs. In glutenites, however, compaction was relatively weak due to the support of rigid gravels, so a large amount of diagenetic fluids flowed through its primary pores and were cemented in a large area. Therefore, cementation is the main factor affecting the physical properties of glutenites. Dissolution is an important factor for the improvement of reservoirs. In sandstone reservoirs, intragranular dissolved pores are produced by the dissolution of plagioclase grains. And in glutenite reservoirs, intergranular dissolved pores and residual intergranular pores are formed by the dissolution of calcite cement. Dissolution fluid is the acidic fluid generated during the maturation of the Permian source rocks. Five types of diagenetic facies are identified in the Qing 1 Member reservoirs in Shinan area, including strong compaction facies, strong cementation facies, mediumstrong compaction and medium cementation facies, medium compaction and weak cementation facies, and medium-strong compaction and weak dissolution facies. The medium-strong compaction and medium cementation facies is predominant. In this area, favorable reservoirs may exist in the channel sandstones of medium compaction and weak cementation facies at the structural highs (e.g. Xiayan 8 well block) and the glutenites of medium-strong compaction and weak dissolution facies in fault development zones (e.g. Shixi 12, Shinan 44 and Shinan 31 well blocks).

Block D in Myanmar is located along the hydrocarbon-richest west deep depression zone in the Ayeyarwady Basin. Presently, high-yield gas flows have been obtained through testing of 3 wells drilled in Taben Formation of Eocene System, indicating that this block has a certain exploration potential. However, this block features a low overall degree of exploration, widespread presence of overpressure in major target layers of Eocene, complicated accumulation conditions and unclear main factors controlling enrichment of hydrocarbon within overpressure system, thus significantly increasing future exploration risks. Through statistical analysis of worldwide representative overpressure hydrocarbon reservoirs and correlated analysis carried out in adjacent counterparts according to the latest geologic knowledge and exploration results regarding Block D, it is believed that two sets of source rocks exist in Block D – Taben and Langshing. The autochthonously developed source rocks of Taben Formation are characterized by shallow buried depth and low degree of evolution. Accordingly, the hydrocarbon is supposed coming from genetic depressions adjacent to the block or the source rock of Langshing Formation deep down. Accumulation inside the overpressure zone in Block D is primarily controlled by reservoir and preservation conditions. The effective migration-transport system and spatiotemporal allocation are important factors for hydrocarbon enrichment. Block D is lack of high-quality reservoirs of Oligocene like in the south Salin depression and its major reservoirs feature medium-porosity, low-permeability sandstone of Taben Formation; therefore, high importance should be attached to secondary pore and fracture intervals in the overpressure system vertically. The lower wall of the fault in Block D is an important area of exploration due to its relatively good hydrocarbon preservation conditions.

Areas around Mahu in the Junggar Basin contain abundant hydrocarbons, suggesting great potentials for exploration. However, low SNRs and resolutions of available seismic data for these areas negatively affect discovery of high-quality reservoirs, verification of lithologic traps and detection of hydrocarbons. In order to address these deficiencies, integration of various sophisticated acquisition techniques was considered for 3D seismic data acquisition in Well Ma-131 Block. By way of simultaneous tests and practical operations, the integration of techniques helped to address the technical problems in remote data transmission, widening of data frequencies, enhancement of data acquisition efficiency, real-time quality control and others. Eventually, the integration solution is successfully promoted and applied in Well Ma-131 Block and other areas, with quality of seismic data improved significantly.

Application shows that the acoustic positioning network is affected by environment, professional equipment, processing methods and artificial factors when it is used for 3D seismic exploration of offshore streamer. In such case, the accuracy of acoustic positioning is reduced, and thereby the quality of seismic data is spoilt. In this paper, some methods for optimizing and improving the acoustical node spacing arrangement, threshold selection, interpolation processing and network adjustment were proposed after the acoustic positioning networks in several offshore seismic areas were investigated. Practice has proved that these methods can reduce the outside effect on acoustic positioning networks, improve the positioning accuracy of streamer acoustic positioning networks and provide high-quality seismic data.

In China, to achieve deflection control while fast drilling with conventional drilling assembly, easing the bit in light pressure and high WOB pre-bending passive anti-deviation technique are often combined to realize hole deflection control in complex formations. However, low weight on bit (WOB) may lead to low rate of penetration (ROP), and high WOB pre-bending passive anti-deviation technique may make the drill string become instable and thereby cause underground complexities. So, for purpose of balancing the relationship among deflection control while fast drilling, ROP and drill string instability, it is necessary to select an optimal WOB. In this study, based on the vertical and horizontal bending beam and column bending theory, a WOB optimization model for deflection controlling and straight drilling with conventional drilling assembly in vertical well was built, which considers the influences of formation deflecting force on well deflection and the minimum comprehensive bit force. Relevant computer program was prepared. Moreover, field test was made in Well BUCS-44H in Missan Oilfield, Iraq. The results show that different range of WOB is applicable to formations with different deflections. In high and steep structures, drill tools with high angle drop capacity are used, and under the condition of pre-bent drill string, high WOB can be adopted to address the contradiction between ROP and deviation controlling and straight drilling. In addition, an optimal WOB is selected by fully considering the deflecting features in formations and those of drill tool itself. In this way, the instability of drill string can be avoided, and deflection control while fast drilling can also be achieved. This study has a certain guiding significance on deflection control on site.