Pilot tests commenced from 1980s in Daqing Oilfield have proved that ASP flooding could improve the recovery rate by 20% based on water flooding, while scaling issue in producers was the only factor which made it hard to reach that objective. Investigation in site indicated that more than 70 percent producers had scaling issues, and scaling types and degree in ASP producers varied dramatically in different wells and different period. In the peak of scaling period, the averaged running life was only a couple of months. A project focused on the harness of scaling issue in ASP producers was implemented from 2002. In the first stage, the study aimed at getting the scaling principle in ASP producers. A series of monitoring and analysis on producing fluid's ion concentration were implemented in different ASP producers. The scale deposited on tubing in different depths were picked out and analyzed. The scaling mechanism of ASP producing liquids in artificial lift systems were created which presented the varying principle of scaling ions as well as the characteristics of scale in ASP producers. A set of scaling principle prediction plates was also created with a success ratio being above 90%. In the second stage, a series of anti-scaling artificial lift techniques were developed including new anti-scaling pump, chemical scale removers and scale inhibitors, and other matching techniques. The new anti-scaling techniques were put into application from several wells up to near 1,000 wells. The operating rate has been improved by 4.13 percent as well as the operating cost decreased by 72.77%. The technical breakthrough in anti-scaling artificial lift systems improved the operating life of ASP producers considerably. It applied solid foundation for ASP flooding to become a beneficial method for mature oilfield development in commercial scale.

Alkali-Surfactant-Polymer (ASP) pilot test with small well spacing and the test with enlarged well spacing for commercial ASP flood are successful in Daqing Oil Field, demonstrating ASP process can greatly enhance oil recovery and bring more economic benefits. However, there are also some problems appearing during ASP flood test, such as serious scale, produced fluids hard to be disposed, and with the well spacing enlarged these two disadvantages might be worse. Therefore, a commercial ASP field test is performed to study performances of ASP flood, scaling characteristics and processing techniques of produced fluids. The five-spot well pattern is adopted in test area, including 18 injection wells and 29 producing wells, and chemical agent, sodium alkylbenzene sulfonate, is produced by Daqing Oil Field. On the basis of laboratory core flood, the formula has been optimized, which can create ultra-low interfacial tension with wide ranges and favorable emulsification. The studies, laboratory core test and numerical simulation, show that ASP system can improve oil recovery 20% more than water injection. At present, polymer injection is following the ASP flood, and the performances from commercial ASP flood are different from those of previous ASP flood. When water cut is slight declined, the injectivity will be greatly increased; the scale is serious for ground equipment, but it is rarely found in the borehole. With the surfactant produced, oil and water separation of produced fluid becomes much harder. The oil recovery enhanced by commercial ASP flood is less than ASP pilot test. If the well spacing is shortened, surfactant performance further improved and ASP system is more optimized, oil recovery efficiency will be further enhanced.

ASP flooding in Daqing oilfield commenced from 1980s. To date, industrial pilot tests have been carried out in three blocks. The averaged recovery was increased by 20%. On the other hand, scaling issue caused high frequent pump failures. Large amount of scale building up in the producers wellbore and downhole equipments with high speed, which resulted in the averaged running life of lifting system decreased from 599 days of water flooding period to 60 days. Further more, some producers’ running lives were only around 30 days, leading to higher production cost and lower production rate as well. Study indicated that, the scaling principle and scale composition in producing wells differed from each other and was difficult to be predicted accurately. In this study, after tracking and measuring the ion in produced fluid for the whole process from water flooding, polymer flooding to ASP flooding and analyzing composition of the scale on different parts of scaling well, the criterion and distinguishing chart of scaling tendency had been set up initially. The criteria were applied in 102 wells in ASP flooding area, the accordance rate was more than 90 percent. Based on that, scaling inhibition technology was timely performed for predicted scaling wells, and the running lives were increased from 40 days to above 200 days. This paper presented the process of the study and is greatly helpful for APS flooding in commercial scale.

The pore structure of sandstone in an oil reservoir is investigated using atomic force microscopy (AFM). At nanoscale resolution, AFM images of sandstone show us the fine structure. The real height data of images display the three-dimensional space structure of sandstone effectively. The three-dimensional analysis results show that the AFM images of sandstone have unique characteristics that, like fingerprints, can identify different structural properties of sandstones. The results demonstrate that AFM is an effective method used to represent original sandstone in petroleum reservoirs, and may help geologists to appreciate the sandstone in oil reservoirs fully.

Because of low volumetric sweep efficiency and large difference in injection and production rate of each zone, the recovery factor of water flooding is very low in some continental and heterogeneous sandstone oil fields, especially when the reservoir continuity is poor, permeability low and high permeability variation between different zones. Due to the amount of incremental producible oil is not large enough to further drill infill wells economically, drilling infill wells and performing polymer flooding simultaneously was proposed and a pilot test has been concluded. The paper introduces the laboratory studies on selection of polymer injection parameters and project design optimization. According to these studies, a pilot test of "Combining Small Well Spacing with Polymer Flooding" was conducted. The well spacing is 100 meters, the zones with a thickness of less than 1 meter and with a permeability rage of 5 to 100 md were combined together and put on development. Both lab studies and pilot results show that the volumetric sweep efficiency was greatly increased, especially after applying separate zone injection measures in polymer injectors based on injection profile surveys and tracer test data. The pilot test indicates that the technique of combining infill wells with polymer flooding is economically feasible with 10% OOIP incremental recovery at a production cost of $10/bbl. INTRODUCTION In continental, multilayer and heterogeneous sandstone oilfields, some reservoirs with poor connectivity and low permeability have lower recovery factors. The low degree of connection of layers between wells and inner-layer interferences lead to high watercut for waterflooding and poor effenciency for increasing the recoverable reserves of single wells. In order to further enhance the oil recovery and increase the oilfield's recoverable reserves, we drilled infill wellpatterns and performed polymerflooding simultaneously to improve the combined economic benefits of marginal reserovir. The main idea of the technology is to adjust the reservoir connectivity by drilling infill wellpatterns, and then inject a polymer solution. On the basis of waterflooding, polymerflooding could further increase some amount of recoverable reserves. The technology of combining dense wellpattern with polymerflooding will not only improve oil recovery but also obtain better economic benefits. Therefore, we implemented the pilot test in the oilfield and also applied separate-layer injection and stimulation measures during the test, which achieved good results with average incremental oil per day for a single well 1.83 times that of the original production, watercut decreased 10.2% and oil recovery increased more than 10%.