The Sichuan-to-East gas transmission project is the first systemic engineering project in China to explore and develop an ultra deep & high acid gas field on such a large scale, which contains natural gas exploration and development, centralized purification treatment, long distance pipeline transmission and comprehensive market development and utilization. It has the prominent characteristics of being oversize, extremely complex, highly risky and extraordinarily difficulty. Based on a brief introduction to the project's development background and construction scale, analyzing the main challenges of technology and management, this paper systematically accounts the construction ideas and the series of achievements of managerial and technical innovation. The construction and management experience of oversize comprehensive natural gas project about the ultra deep and high acid gas field exploration and development series techniques would surely be a useful reference for similar projects.
Facing the development and construction engineering of China's first large gas field with high H2S content and ultra depths, on predecessors' bitter lesson basis, we adhered to the scientific concept of development and adipted a new security concept to fulfill the system engineering, and highlight concept change, standards, supervision and other links. As a result, systematic technologies of safety engineering and development of gas field with high H2S content have been formed, which ensured that the development construction project of Puguang Gas Field can be successfully completed.
The discovery of Puguang Gas Field should be attributed to the innovation of exploration ideas, geological understanding and the development of exploration technologies. By anatomizing the exploration history of Xuanhan-Daxian area, this paper analyzed the formation of structural-lithologic complex trap exploration strategy in Puguang area, expounded the new geological understanding of predictive models of deep-ultra deep high quality carbonate reservoirs and the technical ideas of complicated carbonate reservoir prediction. The discovery of Puguang Gas Field has contributed to the development of deep strata exploration in the Yuanba, Heba and the whole Sichuan Basin, and established the solid resources basis for the "Gas Pipeline from Sichuan to China Eastern Region" Project.
So far Puguang Gas Field is the largest marine gas field in China, which is characterized by high H2S content, ultra depth, strong heterogeneity of reservoir and complicated gas-water relations. There was no precedent for successfully exploiting analogous gas fields in China. During the development and construction of Puguang Gas Field, design of development wells were optimized and some wells with high productivity were breeded via real-time tracking of data of new wells, continuous research on sedimentary microfacies, reservoir prediction and gas-bearing prediction. As a result, a series of design techniques of high effective wells are formed gradually, which provide strong technical supports for high efficient development of Puguang Gas Field.
High H2S and CO2 content, complicated geological condition and field environment brings so many world-classic problems to the exploration and development engineering in Northeast Sichuan gas field. By introduction, research and practice, serial techniques such as drilling, gas test, and completion workover, etc., for the ultra deep and highly acidic gas field were gradually formed. Therefore Puguang Gas Field, for the first time, such reservoir is safely developed in China. This paper introduced these techniques briefly to provide reference for domestic similar gas fields and give many proposals to expand the exploration and development engineering techniques of ultra deep and highly acidic gas field.
The development of Ni-based alloy BG2250 tubing used in severe sour gas field is introduced in this paper. With great efforts in analysing imported similar products, and researching the techniques,such as composition optimization, AOD melting, electro-slag remelting, forging, extrusion, cold rolling, premium thread connection designing and machining, and corrosion evaluation, etc.,the mechanical properties, corrosion resistance and pipe qualities of the Ni-based alloy tubing developed by Baosteel, such as BG2250-125, has reached advanced level compared with other international pipe companies. The Ni-based alloy tubing BG2250-125 has been successfully applied to Puguang gas well, which provides significant guarantee for the severe sour gas field exploration in China.
Puguang Gas Field is the largest high acid marine strata mono-block gas field found in China so far. As the geologic structure is extremely complex, the target stratum is ultra deep, the drilling is rather difficult and high risk, facing so many world-classic engineering problems as high deviation, cavy, blowout, leakage, hard formation, poison, and etc. This paper analyzes the complicated geological characteristics in Puguang gas field, proposes the optimization idea and technique of well structure design and tubing selection, coming up with four casing program optimization schemes according to the knowledge and demand of development, and introduces the application effect and corresponding analysis. The optimization design for well structure achieved to seal off necessary sections of stratum by the simplest casing program, provided the maximum wellbore size,to ensure the cementing quality , meet with the high productivity requirement, and reach the final goal of developing the gas field in a safe and economy manner.
Geological conditions in northeast area of Sichuan are complicated, such as poor drillability in terrestrial formation, severe deviation in high angle structural belt. Pressure system and strata lithology in this area is also complicated, which causes many complex cases and accidents like lost circulation and collapse when drilling. Besides these, this area have "high pressure, high production, high sourness" features. ROP was slow and drilling cycle was long. In order to increase ROP of complicated deepwell in south China, through introducing and developing new technology and new tools, like gas drilling and vertical drilling equipments, combined with existing techniques such as underbalanced drilling, compound drilling, optimum drilling technique system fit for complicated deepwell in northeast area of Sichuan was formed, which improved ROP and wellbore quality of complicated deepwell in south China.
Great achievements had been made on gas exploration on northwest Sichuan province with successful discovery of gas structures such as Puguang and Heba and Yuanba etc. High temperature and hiang pressure and high H2S are typical character of those gas fields. There have several sets of strata pressure systems in land sediment and sea sediment stratums, and the most challenge of cementing job is long cementing section and thin casing annular, and high concentration of H2S and CO2 in gas reservoir will threaten the safety of gas wells. The fair rate of bond quality of intermediate casing cementing and production casing cementing is only 80 % and 72 % separately. By researching and applying Latex anti-corrosion and anti-gas igration slurry and tightly packed heavy anti-gas migration slurry along with techniques such as pump directly with injection opposite for intermediate casing cementing and sector-by-sector surcharging model for designing annular liquid column structure. The bond quality increase highly comparing those before 2006. Referring to Puguang gas field the fair bond is 100 % and good bond 90 %, which has provided safeguard for the gas field putting into production.
There were many characters in marine gas reservoir of the northeast Sichuan, such as deeply buried, high-pressure and high temperature, generally sulfur-containing, production changes significantly in flat and vertical. Which lead to the complicated testing technologies, containing the limited tools, complicated downhole accidents, well-control and the risks of the environment. Based on large numbers of laboratory practices and experiences, well testing technology in high-pressure and high-production sulfur-containing gas reservoir were put forward, including three classes of APR perforating and acid fracturing combined well testing string, string mechanical analysis, multi-pressure control, domestic sulfur resistance and compound surface flow process, which could meet all kinds of testing technology requirements. Emergency schemes and strategies ensure the operation safety, including well killing, blowout prevention and leak proof. These technologies were successfully applied in YB1-C1,YB12 , HB11D and other HPHT sulfur-containing wells, which provided technical support for these gas field exploration.
On the basis of discussing the testing technology for high sulphur gas well and influential factors of data interpretation in detail, we deeply researched and analyzed the blowout path, gas combustion technology, testing flowline and well test interpretation method, and then created a new test process with EE and HH corrosion resistant degree, combustion mode for gas incinerator and modified isochronal test technology. All these technologies have been used successfully in Puguang P302-2, gained reliable test data, and built the modified deliverability equation with these test data. And storability in Puguang Gas Field has been further confirmed by the equation. It is also significant for developing new high sulphur gas field.
It is proved that the design of Puguang gas gathering system is designed with innovation. These aspects, such as technics route, general layout, security design, emergency preparedness and rescue support system are advanced, reasonable and feasible. In particular, the design and integration operation rate of control and SIS(safety instrumented system) is high, and gathering system is controllable and effective. Security design concept are effectively implemented in the following six key issues: advanced transportation technology; reasonable material and device selection; complete control and monitoring techniques; emergency response plans and emergency broadcasting; corrosion control and monitoring techniques; smart pigging technology and general pigging operations. Puguang gathering design projects realized the aims of being domestic first-class and international leading. It can be used as reference for other domestic similar projects.
The corrosion features of highly hydrogen sulfur and carbon dioxide sour gas field were introduced, and the corrosion research results of simulating site operation condition of Puguang gas gathering system during the Puguang Gas Field development were discussed. The corrosion control plan of"carbon steel + corrosion inhibitor + pigging + corrosion monitoring" was expounded which is designed for the Puguang Gas Field with highly hydrogen sulfuer , involuted terrain, a dense population, and a "wet" gas gathering system. The execution effect of corrosion control & monitoring was preliminarily evaluated, and the proposal for some existing problems was given.
Aiming at acute characteristics of flammability, explosibility, causticity, and leakiness of high sour natural gas, giving full consideration to local natural conditions in Sichuan Province and starting with purification process, the paper analyzed process configurations, energy utilization and conservation, safety and environment protection measures. The integrated technology and engineering scheme for high sour natural gas purification was established and successfully used in industrial application.
Based on reef and shoal facies reservoir development characteristics and main controlling factors in Puguang-Yuanba area, the "three step processes method of the facies controlled the reservoir" comprehensive prediction technology of ultra-deep carbonate rock was established, which was under the guidance of sedimentary facies analysis, on the basis of forward modeling and the seismic facies analysis, and by the phase-controlled multi-parameter reservoir inversion as core.
The reserve space of carbonate reservoir is complex and various in Puguang Gas Field, so the traditional hydrocarbon prediction methods can not get better results. The paper used the structural characteristics of seismic data volume to predict hydrocarbon reservoir, which took relationship between seismic data components on each seismic trace (that is structural characteristics of data volume) as study object to research the characteristics of composition and range of various parameters and their relationship with hydrocarbon bearing ability by detecting the amplitude value of each seismic trace, achieving the goal of predicting the hydrocarbon reservoir. Finally, the method was used to predict reservoir of Puguang Gas Field. The applied results demonstrated that the method can overcome the influence of reservoir nature and can get better results in the prediction of strong nonhomogeneous carbonate reservoir.
To deal with exploitation difficulties of North-East Sichuan gas field of the marine strata, after researching extensively, summarizing and promoting the successful experience and failure lesson of project construction technology application scientifically, the SINOPEC Group established an integrated suit of technical company standards system for ultra deep and high acid gas field. The system includes 51 standards, containing geophysical prospecting, drilling, logging, well logging, gas well test and collection, acid gas gathering and transportation system, and HSE (health, safety, environment). It strengthening regulated the project design, recommended the data treatment and explanation method, definituded the required operation and field calibration, standardized the use of technical equipment, effectively guided and supported the construction of safety, quality and efficiency.
Well casings of Puguang Gas Field took place abnormal deformation before and after Wenchuan Earthquake, but the conventional theory was unable to explain it. By seismicity and seismic load analysis, it was concluded that Wenchuan Earthquake was an important factor to the deformation. Seismic load caused static stress change,dynamic load, fault slip, inconsistent deformation between stratums, salt/gypsum creep speedup and casing deformation. The analysis showed that not only the stress size affected the deformation, but also the stress change imposed important influence. Drilling in seismic area should pay attention to the effect of structural stress change.
Puguang Gas Field is characteristic of deep reservior, long hole interval to be perforated and rich H2S. These features brings risks to perforation and operation safety. This paper presents the choice of perforation technology, defination of perforating gun and perforation parameters, selection of sulfide resistance material, tubing protection, design of ignition and detonation propagation reliability related to technical problems and dificulties on perforation operation in Puguang gas field. The perforation effectiveness analysis shows such technical designs can satisfy the requirement of acid fracturing after perforating in Puguang gas field as using anti-sulfur 114 perforators and changing the perforation density. Tubing tripping can be prevented effectively by using some technical measures such as different tubing thickness combination, partition time delayed perforation, combination of longitudinal shock absorber and radial direction shock absorber. Enhancement type fixed bullet system can meet the request of reliable detonation of long-channel perforation.
This Issue
Oct 2010, Volume 12 Issue 10