This paper introduces the recent years' achievements made in China offshore exploration and summarizes the successful procedures and experiences, and analyzes the road to sustainable development for China offshore exploration.
Based on the new finding of Wenchang L low-resistivity light oil field,the finding process,reservoir characteristics and pool-forming pattern were studied. The oil-rock correlation, neritic reservoir type and advantageous migration and accumulation, and new techniques were discussed. The results showed that large amount of hydrocarbon generated by shallow lacustrine mudstone and shale of Eocene Wenchang formation could migrate from sag to Qionghai uplift distantly; neritic shoal-bar reservoir had developed in the 1st member of Zhujiang formation,and dip-sag faults and areal marine sandstone layers of the 1st and the 2nd member of Zhujiang formation had constituted hydrocarbon coursing system in Qionghai uplift; the Dongsha tectonic movement had controlled the late faults by which lower hydrocarbon could migrate upward to upper neritic shoal-bar sandstone vertically. Therefore the vertical migrating accumulating,structure-lithology-dominated, secondary pool-forming pattern were proposed,and it will promote further similar new findings. Finally the enlightenment of explorating new findings was discussed.
Based on the theory of seismic curvature attributes, this paper analyzed features of seismic curvature attributes and found out effective seismic curvature attributes to interpret the seismic data. Suming up the application of the eismic curvature attributes and the notable problems during the process of application,2D curvature attributes explicit physical meanings and obvious advantages in identification of structure characteristics. The attributes are usually related to seismic horizon's geometric shapes(like dip, azimuth and curvature, etc.),which are effective to describe geologic configuration, hierarchy and fault system. Minor faults on general seismic section show the features such as even tiny variety, twist, weaking abruptly of the amplitude.These tiny varieties show small linear structure on curvature attribute of the seismic horizon,so minor faults can be interpreted according to linear structure abnormity. The length of abnormity and directions represent the continued length and directions of faults respectively. The applications show that it is effective and convenient to interpret faults using seismic curvature attributes. The track of the faults and the sizes, shapes and boundaries of sedimentary bodies become continuous and clear. And it is beneficial for fault interpretation.
Although there is a high development potential, the EOR(enhanced oil recovery) techniques of onshore oilfield are not suitable for offshore. Based on the 10 years research and analysis of EOR techniques of offshore thickened oil, a series of resolutions and techniques on driving fluid technology, platform polymer injection distribution technology, production containing polymer treatment technology and effectiveness evaluation of early polymer injection for offshore heavy oil were developed, the system of offshore polymer flooding were established. These techniques had been carried out in Suizhong36-1,Lvda10-1 and Jinzhou with large scale field experiments. The water was controlled at a low level and the oil extraction was enhanced. These works proved the feasibility of the techniques and the value of economy.
Take SZ36-1 oilfield as an example, offshore fields of heavy oil have stepped into later stage in development life and revealed problems gradually for serious injection/production contradiction, big variation for producing reserves in interlayer and plane, much higher for well-controlled reserves, lower for both of oil production rate and oil recovery, changing fast for composite water cut rising and production decline. In view of the challenge for development of offshore fields of heavy oil in China, we put forward the study of comprehensive adjustment for offshore fields in large scale firstly. Because of the special development mode of offshore fields, the proven research thinking and technical route for comprehensive adjustment used by onshore oilfields could not be copied to offshore fields. The research technology of comprehensive adjustment for integral well pattern thickening faces many technical difficulties, so now this research makes a combination of self-characteristics and development mode of SZ36-1 oilfield to put forward a full suite of research thinking and research methods for integral potential tapping and adjustment, and the proposal of comprehensive adjustment for integral well pattern thickening in SZ36-1 oilfield phase I. A water injection well pattern of inverted nine spot is transformed into a well pattern of line drive after pattern adjustment to try a development modes of "direction well & horizontal well network" . The implementation effect of integral well pattern thickening makes a good effect for greatly improved state of water flooding, improved from 80.5 % before adjustment to 91.3 % after adjustment for producing degree of water flooding, forecasting greatly improved recovery for 10.4 %. The technique of adjustment for integral well pattern thickening is sure to be popularized and applied among the similar oilfields.
Complete set of water treatment technology of offshore oilfield was developed to solve the produced water of Liuhua Oilfield, and this technology was applied successfully in Liuhua Oilfield. Research and practice indicated that the technology could inhibit effectively the complicated corrosion caused by H2S,CO2,SRB and solved salts in offshore oilfield. The technology could also reduce the discharge of waste oil, save the cost of run, and insure the treatment of oilfield produced water meeting the environment standard and the long period of safe operation.
From 2002 to 2010, after 8 years' research,we established 10 supporting technologies,for example, indoor screening and evaluating technology of new temperature-resistant anti-salt polymer, reservoir numerical modeling techniques for polymer flooding,polymer injection equipment and technology for offshore platform operations, large displacement polymer section injection technology under the conditions of preventing sands piecewise etc. These technologies were applied in Bohai Oilfield and showed obvious effects in increasing oil precipitation. The successful field tests in Bohai Oilfield indicated that polymer flooding supporting technology was the basis for the successful implementation of polymer flooding. It would make great contributions to the offshore oilfields development effectively.
The article introduced some new production technologies to meet challenges on offshore oil development during carryout of"11th five-year" plan.
This paper summarizes the key technologies and characteristics of offshore oil field development in China by continuous exploration and practice in the offshore oil field exploration, development and production of CNOOC. At the same time, according to the current development of foreign development technology, combined with CNOOC's own characteristics, according to the specific needs of offshore oil field development.
Flexural equation was established in this paper, which was based on application of deepwater drilling riser and Ritz methods in elastoplastic mechanics. Axial tension, inclination angle, lateral gravity components and axial gravity components were considered. Therefore, simple calculation method for natural frequency of drilling riser was achieved. Free-hinged beam was taken as constraint condition of flexural equation combined with drilling string real conditions, which made research approach practical work more. Purpose of research was to provide reasonable design and selection for deepwater drilling riser, and provide a more efficient and applied method, which would show guiding significance for deepwater drilling operation.
Now encryption adjustment wells are getting widely used in offshore, and the risk of well collision increases greatly. Well anti-collision is becoming more and more important. An anti-collision monitoring system based on detecting casing head vibration induced by drilling movements has been build and rig-site utilized. The acceleration sensors were fixed on the casing head to fell the vibration, the time domain analysis and frequency domain analysis were used in signal processing to recognize the approach motive of the drilling bit to the risk case of production well. The result of rig-site test shows that the newly disigned monitoring system can recognize the vibration caused by bit work and detecting the drilling bit approaching the case. It also indicates that the anti-collision monitoring system for detecting casing head vibration is practicable.
Based on the structure and layout of the untended JZ9-3WHPB platform, remote controllable ice induced vibration monitoring system was designed and installed on JZ9-3WHPB platform to record the vibration of the structure so as to learn its dynamic characteristics. Short time Fourier transform was employed to study the temporal variations and mode frequencies of the vibration. Vibration mode was analyzed by comparison of the phase difference between the vibrations of the upper and lower deck and applying bandpass filtering to the signal. Based on the count and analysis of the maximum amplitude and duration of the vibrations, tide and current of the water, and the structure of the platform, the defects of anti-ice induced vibration structure were analyzed, and ice resistant proposals were presented.
To solve the problem of lacking of spare well slots on offshore platform, the adding well slots technology is researched and developed. By analyzing and demonstrating the space condition, the drilling type, structure strength and system capabilities of the old platform, the applicability of the adding well slots was confirmed. The design of the adding well slots was refined and improved, and then it was carried out in the engineering practice.It was demonstrated that the adding well slots can meet the needs of drilling adjust well of old platform with the specialty of simple structure, short project period,low-cost and great economic benefits.
In this study, the floatover technology applicated in platform engineering, fabrication, installation and specific equipment, acility is briefly introduced, through the study of offshore 10000-T class topside floatover technology, and integrating successful application of varied technology in LD27/232/2 oil field development in Bohai Bay. It will be used in guidance of application in 10000-T topside float-over technology in Bohai Bay, and support the application in South China Sea oil and gas field development.
Under the form of LNG sale and purchase in one core, by arranging onshore sale and purchase agreement for liquefied natural gas,CNOOC Gas and Power Trading & Marketing Ltd became one party of the offshore and onshore agreement, which not only kept the consistence of offshore and onshore agreement and reduced the risk for the CNOOC Gas and Power Trading & Marketing Ltd in maxima level, but also passed all the risks smoothly.
Several fundament problems like the mathematical model and numerical simulation of gas production from natural gas hydrate reservoir, similarity principle of gas hydrate physical simulation and exploitation method of gas hydrate reservoir are researched. A mathematical model is developed to simulate the hydrate dissociation in hydrate-bearing porous medium. The model can be used to analyze the effects of the flow of multiphase fluids, the intrinsic kinetic process of hydrate dissociation, the endothermic process of hydrate dissociation, ice-water phase equilibrium, the variation of permeability, the convection and conduction on the hydrate dissociation and gas and water production. For a single gas hydrate reservoir exploited only by depressurization, the study shows that water freezing appears in the formation with the dissociation of gas hydrate under certain condition due to energy deficiency for hydrate dissociation, which can lead to blockage of flow path and stopping of gas production. For a hydrate reservoir underlain by a free gas zone exploited by depressurization, the results show that the overlying hydrate zone can supply an amount of gas to improve the output of production well and evidently prolong the lifespan of gas reservoir. The combination method of warn water flooding with depressurization is proposed, which can comprehensively utilize the advantage of thermal stimulation and depressurization. The method is characterized by a long stable gas production period with a high gas rate.