Jin, Fu (CNPC Engineering Technology R&D Company Ltd.) | Shunyuan, Zhang (CNPC Engineering Technology R&D Company Ltd.) | Bingshan, Liu (CNPC Engineering Technology R&D Company Ltd.) | Bo, Li (CNPC Engineering Technology R&D Company Ltd.) | Lisheng, Chen (Baoding Second Chemical Engineering Factory)
As a kind of methodology to develop coalbed methane in China, RMRS (Rotating Magnet Ranging System) has been popular in SAGD operation in recent years. In Liaohe Oilfield SAGD (Steam Assisted Gravity Drainage) is becoming a more and more mature methodology. In a pair of parallel wells high pressure steam is injected into a horizontal well to drain heavy oil into the lower production well. However, not all thermal resources have not been exploited, such as heat of the hot production fluid, flue gas and hot brine separated by the steam-water separator in the boiler.
Trials and researches were finalized on many dual-horizontal wells in Liaohe Oilfield to learn about the present situation and technical capabilities, while thermodynamic models of various types were established and experimental means were applied to analyze thermal distribution and each of the thermal sources previously mentioned. Effects of various media, flow rates and temperatures on thermal utilization and heat deficit rates were studied on the assumption that one ton crude oil was produced per hour.
Waste heat of flue gas may be utilized to help combust air and the thermo-coil may be used as the air preheater, which improves boiler’s heat efficiency. The high temperature production fluid may be used to heat water in the boiler first and then used as the heat source of the absorption heat pump, so that heat is transferred from the low temperature heat source to the high temperature heat source and the low grade heat energy is recycled. As a high grade waste heat, the HPHT brine that is separated from moist steam in the boiler takes up twenty percent of the total water and shall not be only used to heat injected water. Instead, it may be used to achieve flash evaporation. Thus, waste water is heated and distilled water is recycled.
The waste heat recyling model applies thermo-coil air preheaters to recycle flue gas and flash evaporated hot brine to evaporate waste water. Beside, hot production fluid is recycled to heat boiler water. On a basis of the same fuel consumption volume, the recovery rate and marketability of crude oil are both improved.
Jin, Fu (Petrochina Research Institute of Petroleum Exploration & Development) | Xi, Wang (CNPC Drilling Research Institute) | Shunyuan, Zhang (Petrochina Research Institute of Petroleum Exploration & Development) | Bingshan, Liu (CNPC Drilling Research Institute) | Chen, Chen (CNPC Drilling Research Institute)
Liaohe Oilfield is well-known for wide distribution of heavy oil resoures whose viscosity is around 6.2×104mPa·s (degassed crude oil at 45°C). Heavy oil resources are usually found at the depth of 500-1700m. An integrated research has been completed to study the most efficient utilization of steam huff and puff methodology.
In order to compare the new steam injection method with the conventional EOR method, we selected 7 wells in which steam injection was simulated by software. The high temperature gel particle plugging agents, high temperature frothers and resins were tested. The overall sweep efficiency and oil production rate of these wells were compared with that of adjacent wells that depended on conventional steam injection methodologies.
The multi-well steam injection requires injecting steam into a specific group of wells, so that an overall thermal field may be created. In this way, steam channeling caused by longitudinal heterogeneity of heavy oil reservoirs may be overcome. CO2 has the best role in reducing the oil viscosity, while natural gas and nitrogen follow it. So CO2 is the most appropriate EOR gas. CO2's dissolubility declines as temperature goes up and improves as pressure increases. Temperature of liquefied CO2 varies a lot with different injection speeds, in that the heat diffusion time is different. The faster CO2 is injected, the shorter the heat diffusion time is, which makes downhole temperature change less. As CO2 is injected into formation, it dissolves rapidly with heavy oil and makes it expand. Steam is injected then to heat the borehole, while CO2 diffuses rapidly and its dissolubility declines as temperature goes up, which makes CO2 separated from oil and diffused by scale. Thus, clean-up additives and steam are widely distributed. After shut-in CO2 spreads until it keeps balanced dynamically with viscosity reducers.
The daily production rate used to start to decrease after 5 rounds of steam injection. By injecting steam and CO2 into a group of wells we succeeded in improving the sweep efficiency and production rate.
Jin, Fu (CNPC Research Institute of Petroleum Exploration and Development & CNPC Drilling Research Institute) | Xi, Wang (CNPC Research Institute of Petroleum Exploration and Development & CNPC Drilling Research Institute) | Shunyuan, Zhang (CNPC Drilling Research Institute)
Located in south of Eastern Venezuela Basin, Orinoco Oilfield is the unique huge ultra-tight oilfield that has not been developed by scale in the world. The high-density tight oil is known for its high content of acids, heavy metals and asphaltenes with a viscosity of 1000-10000mPa·s. ML Block whose OOIP is 178*108bbl is situated in east of the oilfield, while cluster horizontal well drilling and cold production technologies are still under research there.
Based on precise geological researches numerical simulation was carried out to optimize cold production of ultra-tight oil with foamy oil flow patterns in horizontal wells, including optimization of well placement, well spacing and horizontal section length. The near-bit geo-steering drilling technology was applied on adjacent wells to test its performance, while an experiment was conducted with PVT apparatuses to examine the effect of pressure decline rates on foamy oil flow. A long core pressure depletion test was accomplished to reveal the effect of foamy oil flow on recovery factors.
Three-dimension cluster horizontal well drilling and completion technologies shall be applied to develop ultra-tight oil reservoirs in huge loose sandstones, with the near-bit geo-steering drilling technology that controls landing points and horizontal sections in real time, keeping the bit move ahead along the lower boundary of the reservoir. Therefore, recovery rates may be dramatically improved due to the gravity drainage of ultra-tight oil. The most appropriate spacing of horizontal wells (500-600m) and horizontal section length (800-1200m) were determined to achieve the maximum recovery rate. The experiment proves that the recovery rate improves as the formation permeability increases, which means the "worm hole" contributes to heavy oil extraction. Boreholes with relatively large diameters, extensive perforated holes and slotted liners may be used to complete wells. In order to take the most advantages of the foamy oil flow mechanism high displacement ESPs shall be used with the selected thinner squeezed at the bottom, otherwise PC pumps with the thinner added at the wellhead are recommended.
Cold production technologies applied in ML Block save the overall production cost by 15.2%, improving the ultimate recovery rate by 8.6%. The foamy oil flow theory is improved, while it is the first time to integrate foamy oil flow production technologies with cluster horizontal well drilling technologies and near-bit geo-steering drilling technologies. As a result, the overall production rate of tight oil was greatly improved and the average production life of wells was extended.
Buried in loose and fine-grained sandstones, heavy oil is widely found at the depth of 3256-3417m in Block KM Yumen Oilfield, China, taking up 4.1 square kilometers. It is known for its low permeability (25.97∗10-3μ m2), high density (0.973kg/L) and viscosity (12708mPa•S). There is a thick interlayer above it, while an aquifer is only 3m beneath it. Thus, fractures may extend downward and perforate the aquifer, which causes water fingering.
Effects of propped fractures of various shapes and their conductivities on production were simulated via ABAQUS, therefore the fracturing scale and appropriate fracture shape were selected. Flow resistance tests were applied on many applicable diverting agents in the lab and the high density diverting agent FJ was selected. A small scale fracturing experiment was carried out prior to the hydraulic fracturing operation, so that stratigraphic properties and the fracturing fluid's performance could be studied in advance.
Based on the curve of production rates affected by propped fractures with various shapes and conductivities, short and wide fractures with a conductivity of 60μ m2•cm shall be adopted. The environment temperature of fractures goes down as the water based fracturing fluid enters the reservoir, which increases the viscosity of heavy oil and restricts formation fluids from penetrating fractures. Therefore, the benzene organic solvent shall be used as a spacer fluid to isolate tight oil and the fracturing fluid. In order to keep fractures from extending downward and damaging the aquifer, an artificial isolation zone is established by the high density diverting agent FJ that builds up a solid low-permeability interval along the low edges of fractures. The low density ceramsite is optimized and used as the proppant. In the fracturing experiment the benzene organic solvent is pumped first to make fractures while isolating heavy oil, then active water with the high density diverting agent FJ enters the reservoir to build up the protection zone. The displacement fluid is pumped to push FJ into fractures. The well is shut in for 10-15 minutes prior to sand fracturing in order to make FJ distributed evenly.
Wells in the region used to be developed intermittently, while the above integrated technologies improved the daily production rate by 2.63 times and it has stayed 8-10t/d since the last 6 months. Integration of the spacer fluid, fracture control technique and proppant optimization significantly contributes to heavy oil exploitation in KM Block, Yumen Oilfield.
Jin, Fu (CNPC Drilling Research Institute) | Shunyuan, Zhang (CNPC Drilling Research Institute) | Bingshan, Liu (CNPC Drilling Research Institute) | Weiwei, Yin (China United Coalbed Methane Corporation, Ltd.) | Chen, Chen (CNPC Drilling Research Institute)
It is estimated that tight oil takes up 46% of the total reserve volume, including conventional tight oil, super-tight oil and ultra-tight oil whose viscosity is 5.8×104mPa·s (degassed crude oil at 50°C). Some tight oil resources are 600-900m deep, while others are found in deep formations (1300-1700m). In order to deal with sand production and low recovery rate integrated researches on super-tight and ultra-tight oil buried in deep formations have been accomplished.
A group of 7 wells were selected and the overall steam stimulation was simulated by software. All modified chemicals such as the high temperature frothers, high temperature gel particle plugging agents and special resins were tested in labs in order to prove their performance, while downhole tools had been applied in adjacent wells. At last the average sweep efficiency and oil production rate of wells in the group were compared with that of adjacent wells.
Casing programs, horizontal sidetracking technologies and slim hole cementation technologies shall be optimized to extend the well's life. The multi-well steam stimulation technology which depends on injecting steam into a group of wells and creating a uniform temperature field is useful, as steam channeling caused by longitudinal heterogeneity in the tight oil reservoir and repetitive steam injection may be overcome. Mechanical interval selection technology and vacuum heat insulation pipe are recommended to obtain steam of appropriate volumes. Various high temperature frothers and gel particle plugging agents shall be applied to adjust the steam injection and production profile, improving the sweep efficiency. Liquefied carbon dioxide and other cleanup additives may be injected before steam as more water comes out and remaining oil keeps farther away from the borehole after repetitive steam huff and puff. Fracturing and sand exclusion may be achieved at the same time by squeezing special resins into formation while fracturing. Sand may be controlled by artificial boreholes, optimized liners and flushing foams. Series of drilling and production technologies have been optimized, therefore the average sweep efficiency and recovery rate of single wells in the group were improved by 12.52% and 13.23% respectively.
Conventional steam stimulation used to be adopted by scale in Block CH, while the daily production rate began dramatically decreasing after 4 to 5 rounds of steam injection. The integration of multi-well steam stimulation technology, mechanical interval selection technology, vacuum heat insulation pipe running technique and optimization of chemicals and gases improves heat utilization and sweep efficiency. While the optimized drilling and completion technology improved the quality of horizontal wells.
Jin, Fu (CNPC Drilling Research Institute) | Shunyuan, Zhang (CNPC Drilling Research Institute) | Bingshan, Liu (CNPC Drilling Research Institute) | Chen, Chen (CNPC Drilling Research Institute) | Shifei, Dong (Daqing Oilfield Huayu Industrial Company) | Weiwei, Yin (China United Coalbed Methane Corporation, Ltd.)
SAGD technology has been applied by scale in Liaohe Oilfield China, where high pressure steam is injected in a horizontal well to drain tight oil into the lower production well. However, much waste heat has not been exploited, including heat of the hot production fluid, flue gas and HPHT brine separated by the steam-water separator in the boiler.
On-field researches were carried out on many dual-horizontal wells in Liaohe Oilfield to learn the present operation situation and technical capabilities, while thermodynamic models of various types were established and experimental apparatuses were utilized to analyze the present thermal distribution and each of the above waste heat sources. Effects of various media, flow rates and temperatures on heat utilization and the heat deficit rate were studied on the assumption that 1t crude oil was produced each hour.
The high temperature production fluid may be used to heat water in the boiler first and then used as the heat source of the absorption heat pump, so that heat is transferred from the low temperature heat source to the high temperature heat source and the low grade heat energy is recycled. Waste heat of flue gas may be utilized to help combust air and the thermo-coil may be used as the air preheater, which improves boiler's heat efficiency. As a high grade waste heat, the HPHT brine separated from moist steam in the boiler takes up 20% of the total water and shall not be only used to heat injected water. Instead, it may be used to achieve flash evaporation. Thus, waste water is heated and distilled water is recycled.
The optimized waste heat recyling proposal applies the thermo-coil air preheater to recycle flue gas, flash evaporated hot brine to evaporate waste water and high temperature production fluid to heat boiler water. On a basis of the same fuel consumption volume the recovery rate of crude oil is enhanced by 31% and marketability of it is improved by 8.6%. More energy is saved and recycled, which contributes to the green oilfield construction.