Summary Horizontal wells are widely drilled to produce heavy oil because of their large reservoir contact. For example, there are more than 500 horizontal wells operated in cyclic-steam-stimulation (CSS) or steam-assisted gravity-drainage (SAGD) processes in Liaohe oil field. The length of these horizontal wells usually ranges from 100 to 500 m. But it is challenging to recover oil along a horizontal well proportionally by conventional steam-injection processes because of poor steam conformance along the horizontal well, which is derived from reservoir heterogeneity, large horizontal-well length, and steam properties. Field investigation shows that only half of the reservoir along the horizontal well is well steamed and recovered, and that the average ratio of oil production to steam injection (OSR) is less than 0.28. In this paper, a separated-zones steam-injection process is introduced to improve steam conformance along the horizontal well; in this process, in which packers, outlets, pressure-sensitive valves, and ball sealers are involved, steam could be injected to the selected zone, separated dual zones in sequence or at one time, or separated multizones simultaneously. In order to investigate steam conformance along the horizontal well and feasibility of separated-zones steam injection, primary laboratory experiments with a sand-packaged model, numerical simulation, and field testing are carried out. These show that steam injected to separated zones could be regulated with sealed packer(s) based on the principles of steam crossflow and superimposing the effect near the packer; therefore, steam conformance along the horizontal well could be considerably improved by separated-zones steam injection. Field testing of 76 wells stimulated by separated-zones steam injection shows that up to 70% of the reservoir along the horizontal well is well steamed on average, and steam conformance is significantly improved.

Summary There are a lot of sludges produced in oil production and storage processes in Liaohe Oil Field. Usually complicated chemical processes are involved in treating the sludge effectively and such surface-treatment processes are subject to high cost and environmental challenges. Therefore, the feasibility and performance of sludge injection into steam-stimulated wells, and sludge sequestration and associated heavy-oil-recovery improvement are investigated on the basis of results of laboratory research and field operation. The sludge originally produced from the reservoir comprises mainly water, some oil components, and solid phase such as mud and fine sand, and aggregation of the injected sludge components, except water, could block the void porous space. Actually, the sludge is buried into its origin, the reservoir. As the sludge is injected into the steamed reservoir through an enlarged pore at high injection pressure, the permeability of the formation could be significantly decreased (the permeability reduction rate could be more than 98% after sludge blocking in our experiments with sandpacked tubes), and the sludge blocking performance is related to the reactions of oil and solid separated from the sludge, including adherence to the sand surface, consolidation of the sands, and filling in the void porous space. Consequently, the sludge is stored in the steamed formation, and the water in the sludge is separated and produced. At the same time, steam conformance and heating efficiency could be improved by implementing a sludge blocking process, thereby significantly improving oil production. Sludge sequestration has been applied to 45 steamed wells in Shuguang Oilfield until 2018, and all the wells have been stimulated by 7–10 cycles of CSS process. The total sludge injection of the wells is up to 133,200 tons, and more than 15,000 tons of oil and solid separated from the sludge are deposited underground. At the same time, more than 20% increase in cyclic oil production on average is obtained by the sludge-injection process.

Horizontal well steam injection is effective to recover heavy oil for its large reservoir contact. To date, more than 150 horizontal wells have been drilled in Shuguang oil region, most of them are operated in steam stimulation and SAGD processes, and completed with slotted liner at length from 100 m to 500 m. But it is much challenging to recover oil from reservoir along horizontal well proportionally because of steam characteristics, large well length and reservoir heterogeneity. Results of simulation and field temperature testing show that only about half of reservoir along horizontal wellbore is recovered well, and average OSR (defined as ratio of oil production to steam injection) is less than 0.28, and it is not satisfying for the large cost of horizontal well drilling and completion. Furthermore, steam crossflow between wells and pressure depletion in local reservoir well steamed could also result in reduction in oil production and OSR. To improve horizontal well steam injection, separated-zones horizontal well steam stimulation technology is developed, in which temperature sensitive packers, outlets, pressure sensitive valves and ball sealers are involved. The steam injection of different zones separated by packer(s) could be regulated or controlled according to engineering design. There are four techniques developed including dual-zones steam injection in sequence or at one time, selected zone steam injection, and simultaneous multizones steam injection. In order to investigate temperature and steam injection of different reservoir zones along horizontal well in different steam stimulation process, experiment, numerical simulation and field testing are carried out in past three years. In this work, laboratory experiments are carried out with large simulation apparatus packed with sampled oil sand and equipped with temperature sensors and pressure sensors at first. Secondly, structure of steam injection pipes and steam injection scheme are optimized based on numerical simulation, and primarily reservoir selection requirements are also provided. Thirdly, result of application of separated-zones steam injection to 76 wells and monitoring of temperature and pressure is presented, and considerable improvement of steam injection and heavy oil recovery obtained. At last, the future of intelligent separated-zones horizontal well steam injection is prospected.

As a new potential mean of artificial lift production, production using progressive cavity pump (PCP) has many advantages such as energy saving, lower first investment, and convenient in management. However, it is more challenging to implement this lifting method to thermal production of heavy oil for the temperature limitation of elastomer stator and bonding agent, and hostile temperature vibration in the wellbore environment, as a result, up to date, there is no application of PCP to thermal heavy oil production in Liaohe Oilfield which is the largest heavy oil field in China.An applicable thermal PCP developed based on extensive testing is introduced in this paper. It involves an applicable thermal fluororubber stator and bonding agent which could operate under high temperature conditions (up to 210℃) enough for the thermal requirement of steam injection, and great temperature vibration condition in the wellbore ranging from 80℃ to 210℃. The whole top-drive thermal pumping unit is designed in consideration of thermal wellbore environment in heavy oil production procedure of steam stimulation.The thermal PCPs have been applied to 5 wells and detailed field testing dynamic is monitored and investigated. Favorable performance of the thermal pumping unit is observed in the rugged production environment (the measured wellbore fluid temperature is up to 165℃) for more than 6 months, and the pump efficiency is about 60%~70%. Compared with the conventional rod pumping lift production, about 20% increase in periodical cumulative oil production and 50% lower horsepower requirements is obtained.In summary, the developed thermal progressive cavity pump is feasible for heavy oil production in steam stimulation process, which could operate under extensive temperature range, and the upper limitation is up to 210℃.

There are a lot of sludge generated in oil production and storage processes, usually complicated chemical processes are involved to treat the sludge effectively, and high cost and environmental pollution are always extremely heavy burden for Liaohe Oilfield. Therefore, the feasibility and performance of sludge injection into steam stimulated wells, and sludge sequestration and associated heavy oil recovery improvement are investigated based on results of lab research and field operation. At first, the composition and rheology of the sludge samples from Liaohe Oilfield are measured and analyzed in detail. Secondly, the injection, sequestration and block performance are investigated by sand pack experiments, particularly the aggregation and blocked sand are analysed by scanning electron microscope, and improvement of heavy oil recovery by sludge injection. Thirdly, the principles of sludge sequestration and associated heavy oil recovery improvement are discussed. At last, field application of sludge in Liaohe Oilfield is presented. As we know, the sludge are produced from the reservoir, it is comprised of mud, fine sand, some oil phase components and water. Aggregation of the sludge components except water is potential to block porous media such as produced formation, at the same time, the sludge are buried in its origin, the reservoir. The sludge is injected to produced reservoir through enlarged pore at high injection pressure, and aggregated mud, fine sand and oil from sludge could consolidate formation sand and block pores effectively after injection process (permeability decease of sludge blocked sand tube is more than 90%). As a result, the sludge is stored in steamed formation, and separated water could be filtered and produced. At the same time, steam conformance could be improved by stored sludge, accordingly heavy oil production is increased. Average oil production increase of 45 wells in Liaohe Oilfield is more than 20%. Substantial sludge are treated by such subsurface sludge sequestration in steamed heavy oil reservoir, and sludge sequestration in other reservoirs are evaluating as well.