SPE Advanced Technology Series

The paper summarizes the methods and effects of cyclic waterflooding in the southern oilfields of the Daqing Placanticline, discusses the feasibility and necessity of this process in lower permeability reservoirs, and analyzes systematically the main factors which impact the results of cyclic flooding. Production performance is compared and contrasted for fields developed by both conventional and cyclic waterflooding. Based on field case histories, the impact of cyclic waterflooding on performance at different water cuts is evaluated. It is demonstrated that cyclic flooding should be implemented at low water cuts, but is beneficial at all development stages. Cyclic waterflooding is an effective measure to enlarge sweep volume and enhance conformance efficiency and oil recovery. The practices described can provide guidance for cyclic waterflooding in similar oilfields.

Since 1980, the oil production of Daqing oilfield has been at high water-cut stage. The rate of oil production has naturally decreased. Research was undertaken to maintain and enhance fracturing effects on oil production, including strengthening the preparation for fracturing and management after fracturing. Properly selecting the wells and zones for fracturing is important. Pre-treatment of injection wells and restoration of reservoir pressure can improve the results of fracture treatments in producing wells. Fracturing techniques were also developed for multiple thin intervals. This paper uses examples from the Lamadian Oilfield of Daqing.

This paper describes development and applications of separate layer production technology, which facilitates full exploitation of the potential of each oil-bearing layer. The technology has evolved as water cut has increased in Daqing oilfield and focus has shifted to thinner, lower productivity layers. In Daqing field, 11 kinds of separate layer water injection strings, which can be divided into two main categories (hydraulic inflatable and compressional), 33 kinds of separate layer production (water shut off) strings divided into four main categories (including integral, slip support releasing, drill-able and pressure balance), four separate layer fracturing techniques (including sleeve separate layer, limited entry completion, multi-frac and positioning balance) have been developed.

This paper summarizes the composition, principle, properties and field application effects of blocking agent in the technique of singlefluid water plugging using AP4 polymer. Both the laboratory investigations and field application show that the blocking agent has some distinct advantages, such as shallow and firm plugging effect, low cost, simple process and easiness of being removed when necessary.

This technique including explosive reforming and explosive welding is mainly adopted for repairing downhole damaged casing in an oilfield. It is based on the principle of explosive action to restore a deformed casing and to weld the damaged section.

Logging technology for determining production profiles through casing/tubing, the small diameter series of designing tools, and the advanced logging techniques is described. Applications of the logging technology are demonstrated using typical examples.

Daqing Lamadian oil field is the largest oil field with a gas-cap in China. Monitoring, controlling and adjusting techniques have been used extensively to minimize cross flow. An inverted nine-spot pattern was used in the oil-bearing area. Gas-bearing layers were not perforated and there was a 400 to 600m buffer zone of oil and gas migration left between oil- and gas-bearing areas. A monitoring system for gas-cap performance was established. Flow between the oil-bearing and gas-bearing layers has been successfully controlled and a relatively stable oil-gas interface has been maintained for 20 years.

Using the principles of seepage mechanics, this paper analyzes the interrelationship between formation pressure and injection-production ratio and the influential factors. On the basis of a mechanical study, it quantitatively analyzes the pressure history of each area by means of a mathematical statistic method and the controlling factors, and the effect of every factor on formation pressure. It furnishes a scientific basis for the effective and rational control of the Southern development area of the Saertu Reservoir and each sub-area. Introduction

Injection-production ratio is a composite index, which reflects the balance condition of injection and production, characterizing the relation between fluid-withdrawal rate, water injection rate and formation pressure during waterflooding in an oilfield. It is also an important index to program and design the water injection rate. Reasonable injection production ratio can maintain formation pressure, so that the oilfield can have vigorous ability to produce fluid and oil, reduce ineffective energy consumption and improve oil recovery. Therefore, injection-production ratio should be regulated in accordance with the geological features of the oilfield and the development conditions, such as the active control of the formation pressure level, which is important in the optimization of the whole injection-production system, and is of great significance to the scientific development of the oilfield. The development principle of waterflooding at the early stage is to maintain formation pressure. However, with the development of deep reservoirs and taking various measures to tap oil potentials, especially successive development of different types of reservoirs, injection-production ratio of the oilfield has greatly changed. The previous procedure of keeping the injection-production ratio around 1.0 has been unable to maintain the desired formation pressure. The control of the injection-production ratio of the oilfield, and the relation between the injection-production ratio and formation pressure has problems to be resolved during further production in southern development area of Saertu Reservoir. Practical performance knowledge of the field, and history matching by means of a mathematical statistical method have shown the quantitative relations between the influential factors of the Southern development area of Saertu Reservoir and each sub-area.

Establishment Of Mathematical Model Between The Formation Pressure And Injection-Production Ratio Of the Oil Wells

The formation pressure usually used in the material balance equation is the average formation pressure of the whole reservoir system. It is different from the oil well formation pressure usually used in the development performance analysis.

Using the principle of fluid mechanics and the geometric properties of the annuli in directional wells, the law of laminar helical flow of drilling fluid in eccentric annuli was studied. Analytical solutions of apparent viscosity, velocities, flow rate, pressure drop and the stability parameter are presented. Results of numerical simulations are given. Laboratory studies and field application in eleven wells of Daqing oil field were used to validate the theory. A method for calculating pressure drop in annuli, which can be used in designing hydraulic parameters of directional wells is given.

Based on lab data this paper summarizes differences of petrophysical parameters of sandstones in Daqing Oil Field which were not watered out before waterflooding and were watered out after waterflooding. Pore throat dimensions, relative permeability, and wettability change with prolonged waterflooding. Using internal waterflooding at an early stage is a method of maintaining the reservoir energy and achieving long-term high and stable production. Injecting a great quantity of water for a long time is an effective means of enhancing oil recovery of reservoirs for Daqing Sandstone Oil Field.