Zhao Fulin

In-depth Profile Control Technologies in China—A Review of the State of the Art

Abstract In the process of waterflooding and polymer flooding, the oil displacement efficiency is poor because of the heterogeneity of reservoirs, the conventional profile control and water shutoff technology can no longer satisfy constantly production demand. So, in-depth profile control technology has been developed in recent years, and an obvious effect is obtained in improving development effects of waterflooding and polymer flooding in high water-cut stage. In this article, in-depth profile control technology is widely analyzed, and a development tendency of this technology is proposed; that is, a complete study of in-depth profile control and polymer flooding should be developed based on the sufficient understanding of reservoir status, advantage channels should be controlled and fluids diverted, and the oil displacement efficiency of waterflooding and polymer flooding for high water-cut stage could be improved.

A Study on Mass Concentration Determination and Property Variations of Produced Polyacrylamide in Polymer Flooding

Abstract Because injected polyacrylamide often quickly breaks through to production wells during polymer flooding, its mass concentration determination is very significant. However, due to the variations of relative molecular mass and degree of hydrolysis of produced polyacrylamide, the conventional determination methods, including viscosimetry and starch-cadmium iodide colorimetry, are no longer suitable for determining its real mass concentration. A new determination method—ultrafiltration concentration film drying—is proposed and developed in this article. By purifying and concentrating produced polyacrylamide solution using an ultrafiltration system and then dehydrating water to a constant weight, this method can determine the mass concentration directly. This method has been evaluated in the laboratory and compared with two conventional determination methods, verifying its adaptability and high accuracy. The produced polyacrylamides from three different polymer flooding blocks have been determined using this new method. The results show that the relative molecular mass of produced polyacrylamide decreased greatly and its degree of hydrolysis increased obviously. The reasons and differences have been also analyzed. These corresponding variations make the results determined by the conventional methods much lower than the actual results, and it is implied that the previous methods need to be improved or replaced.

Residual Polymer Reutilization for IOR after Polymer Flooding: From Laboratory to Field Application in Daqing Oilfield

Abstract According to the reservoir condition of the Lamadian block for polymer flooding in Daqing oilfield, the optimized flocculating agent was studied in order to fully use residual polymer in formation and improve oil recovery after polymer flooding. The experimental results showed that stabilized sodium clay is the best flocculating agent and can react with residual polymer to form a floc unit for improved oil recovery (IOR). Using atomic force microscopy, we can see that the flocculating agent can react with residual polymer to form a floc unit and one clay particle usually reacts with four to seven polymer molecules. This residual reutilization technology was applied in six injection wells of Lamadian in Daqing oilfield; the six injection wells had 13 connected production wells with an average water cut of 95.5% and produced polymer concentration of 459 mg/L. About 30,971 m3 flocculating fluid with 842 tons of flocculating agent was injected into the six injection wells. After treatment, the injection pressure of injection wells was increased and the injection profile was improved; the water cut of the connected production wells was decreased and the oil production rate was increased. The oil increment was 3.6 tons/day, the water cut decrement was 2.5%, and the produced polymer concentration decrement was 89 mg/L. By March 2008, the accumulated oil increment was 2,878 tons and the input–output ratio was 1:3.33.

The Application of Oily Sludge in Chinese Oilfield

Abstract Using industry wastes for conformance control has recently attracted significant interest—in particular, when using oily sludge for in-depth fluid diversion. About 500 tons of oily sludge is generated from oil production, transportation, and refining each year. Oily sludge is mainly composed of oil, water, o/w emulsions, and solids and is quite difficult to separate and reuse. The accumulation of oily sludge has posed a serious environmental problem. Additives such as suspension agents, dispersion agents, and viscosity thickeners are often added into oil sludge as conformance control agents to extend particle suspension time, increase plugging efficiency, disperse oily drop, and increase penetration depth. The advantages of oily sludge as conformance control agents include: (1) good compatibility with formation; (2) high temperature resistance; (3) high salinity resistance; (4) low costs; and (5) environmental protections. This method has been used by most oilfields in China, with better results.

A Study on Bottom Water Coning Control Technology in a Thin Reservoir

Abstract The conventional method to control bottom water coning by perforating and setting a packer is not suitable for a thin oil reservoir, because it is hard to determine the perforation interval and place the packer accurately; thus, a novel technology has been proposed and developed in this article that can build up a gel packer in a thin reservoir by gravity segregation. The working fluids including high-density brine, selective blocking agent, and overplacing fluid were studied to form a gel packer, which is caused by gravity segregation resulting from density differences among oil, water, and working fluids in the water–oil transition zone and is used to control bottom water coning. The progress and the mechanism of control of bottom water coning using the novel technology by visual physical simulation experiments is also shown. By December 2008, this technology had been successfully applied in 38 wells of Luliang oilfield; the accumulated oil increment was 20,220 t, the accumulated water decrement was 72,880 m3, the water cut declined from 11.3 to 38.4%, and the input–output ratio was up to 1:2.41. The success of field tests confirmed that this technology is quite suitable for controlling bottom water coning in a thin reservoir and has a broad application prospect.

Study and Application of In-depth Water Control Technology for Production Wells

Abstract In view of low oil increment and short valid period of conventional water shutoff for production well, the authors propose and develop a new in-depth water control technology for production well. The different-strength (from weak to strong) water shutoff agents are separately injected into a remote zone, transition zone, and near-wellbore zone in this technology, which can achieve the aim of in-depth water control, extending the valid period of water control, increasing oil production, and decreasing water cut. Physical and visual simulation experiments show that there is optimized displacement of 3:10 between production well and injection well for the water shutoff agent with the most oil recovery. Field tests in Jidong, Shengtuo, and Weizhou 11-4 oilfields also show that the in-depth water control technology is a reliable, feasible technology and worthy to be widely applied.

Study on Components and Formulation of Liquid Gel Packer in Air Drilling

Abstract Air drilling is widely used in oilfields at home and abroad due to its ability to increase drilling speed significantly, reducing the drilling cost, protecting the formation effectively, and improving success rates in exploration. However, water breakthrough in formation is so serious that traditional methods of water shutoff cannot meet the demand of plugging while drilling, which restricts the application of air drilling. Based on the investigation and analysis at home and abroad, this article develops a new technique on blockage of water influx to the wellbore in air drilling. The technique involves the research and application of a kind of gel system used as a packer; that is, a liquid gel packer. The formulations of the gel packer, its effecting factors, and its loading capacity are studied at varied temperatures of 30°C–70°C. The study shows that the breakthrough pressure of the gel packer can reach 20 MPa, and materials such as sodium soil, scrap iron, and kaolin, which may exist in formations, can barely affect the gelation time and gel strength. All experimental results prove that the liquid gel packer has an excellent strength and wide suitability.