The Chinese government is seeking CO2 gas emission reduction measures. CO2 capture and geological sequestration is one of the main measures. Injecting CO2 into oil reservoirs can not only achieve the environmental protection purpose of CO2 geological sequestration but also improve oil recovery and realize economic benefits, which helps to offset the cost of CO2 sequestration. Therefore, the oil reservoir is one of the best sites for CO2 sequestration. As for the reservoir of CO2 flooding after water flooding, there are two methods for evaluating the potential of CO2 enhanced oil recovery (EOR) and sequestration capacity, which are the mass balance method and analogy method. Through a combination of these two methods, this paper presents a new method, which can be reasonably used to evaluate these potentials. Besides, the screening criteria of CO2 sequestration and EOR in the Junggar Basin are also proposed. On the basis of the guidelines of CO2 source matching, reservoir characteristics, and fluid characteristic, four typical low permeability reservoirs (Caiman oil reservoir, Karamay oil reservoir, Beisantai oil reservoir, and Luliang oil reservoir) of the Junggar Basin are selected to study their potential of CO2 EOR and sequestration. And then the potential of CO2 EOR and sequestration capacity for the Junggar Basin oil reservoirs of CO2 flooding after water flooding is studied by applying the method mentioned above. For 275 development blocks of 24 oil fields in the Junggar Basin, 139 development blocks are suitable for CO2 miscible flooding EOR and sequestration, whereas 136 development blocks are suitable for CO2 immiscible flooding EOR and sequestration. The total EOR potential could be 18 407.76 × 104 t and the CO2 sequestration potential could amount to 47 486.0 × 104 t. The evaluation results show that the Junggar Basin’s oil reservoirs are suitable sites for CO2 EOR and sequestration and have great potentials. It can provide the decision basis for the future implementation of CO2 emission reduction projects in Western China.

After more than 20 years’ development, S oilfield has entered high water cut stage. The layer contradiction is prominent and the water flooding condition is complex, which result in the complex decentralized state of the remaining oil. In order to determine the remaining oil distribution to guide the comprehensive adjustment of the oilfield, the reservoir architecture analysis of delta front was conducted. Based on the core, seismic data, dense well logging data and production performance data, the reservoir architecture of delta front in Dongying group is characterized with hierarchy process, model guidance and numerical simulation methods. In the paper, the distribution style of interlayers in single mouth bar is discussed. The distribution feature of the remaining oil under the control of interlayers is analyzed. It shows that multiple main channels form continuous mouth bar complex and single mouth bar develops several accretions. Interlayers in single mouth bar express in two forms: the foreset type along the source direction and the arch type perpendicular to the source direction with a low angle from 0.4° to 1.0°. Along the source direction, remaining oil gathers inside accretions whose injection-production does not correspond under the control of interlayers. And the remaining oil is enriched at the front of accretion. In the vertical source direction, the remaining oil accumulates in the high part of accretions. Under the guidance of remaining oil distribution characteristics controlled by reservoir architecture, one horizontal well was deployed. The average output is more than 100m3/d and the water cut is under 30%, which indicates the effect of this reservoir architecture analysis work. The successful implementation of the horizontal well demonstrates the vital function of the reservoir architecture research for this kind of mature oilfield. This will also be one promising research direct for the overall adjustment and remaining oil tapping.

This paper proposes a set of methods for selecting the type of sand control screen and optimizing the accuracy in heavy oil Wells, which take into account the requirements of sand control and productivity protection in heavy oil Wells. Sand retaining experiments are carried out with slotted screen, wire wrapped screen and metal filter screen under the condition of oil and water mixed sand carrying flow. In order to optimize the sand control screen suitable for heavy oil well, this paper uses the weighted average method to quantitatively evaluate the flow performance, sand retention performance and oil conductivity of the screen. Then, repeat the experiment by changing the accuracy of the screen to optimize the accuracy. The experimental results show that the permeability of the three kinds of sand control screens is about 2μm2 when only heavy oil plugging occurs. Under the combined plugging action of formation sand and heavy oil, the slotted screen has the highest permeability, and its conductivity to heavy oil is 10% higher than that of the other two screens. The silk-wound screen has the best sand retention performance, with a sand retention rate of more than 90%. Through the quantitative evaluation of the sand control performance of three kinds of screens in different production stages of heavy oil Wells, the slit screen is selected as the optimal screen. For simulated formation sand with a median particle size of 250μm, the optimal sand control accuracy is 200μm. This paper provides a quantitative optimization method of screen type and accuracy for sand control design of sand-producing heavy oil Wells, so as to maximize the productivity under the premise of ensuring sand-producing control of heavy oil Wells.

No abstract

There is abundant heavy oil resource in Bohai Oilfield and steam stimulation has proven an effective method through several field pilots. Till now, all steam stimulation is conducted by two-trips string for steam injection and oil production individually. That is, when the process of steam injection, soaking and blowout is finished, an oil production string will replace the downhole string through workover operation. According to statistics, the operating charge in one huff-and-puff cycle is more than 2.5 million Yuan. Besides, workover operation takes more than 26 days and results in about 1000 m3 kill fluid leak, which greatly reduce the thermal recovery effect. Considering the drawbacks of two-trips string technology, a new injection-production integrated technology by jet pump, namely single-trip string realizing steam injection and oil production, is developed, which includes downhole string system and surface technological process system. The downhole string provides passages for steam injection and oil production. The temperature and pressure resistance of string system could reach as high as 350°C and 35MPa, respectively, which can adapt to the high temperature environment during steam injecting. The surface technological process system can separate 279m3/d producing fluid and supercharge the power fluid as high as 25MPa, which meet the needs of thermal well production. The new technology tested in X well. More than 6000 m3 steam with 356°C temperature and 16MPa pressure was injected. The downhole string system and Christmas tree withstood the HTHP test and kept in good condition. During oil production, the surface technological process ran run steadily. The pressure of plunger pump was up to 20MPa and more than 120m3 produced fluids were separated by the separator. Compared with two-trips string technology, the new technology saved 2 million Yuan and 21 operating days. Besides, no kill fluid leaked, which improves thermal recovery effect. This is the first time that injection-production integrated technology for steam stimulation is developed and put into field trial. The favorable application result indicates that this technology will promote the high-efficient exploitation of heavy oil in Bohai Bay.