In-Depth Fluid Diversion by Pre-Gelled Particles. Laboratory Study and Pilot Testing.
- J.-P. Coste (RIPED-CNPC) | Y. Liu (RIPED-CNPC) | B. Bai (RIPED-CNPC) | Y. LI (RIPED-CNPC) | P. Shen (RIPED-CNPC) | Z. Wang (SINOPEC) | G. Zhu (SINOPEC)
- Document ID
- Society of Petroleum Engineers
- SPE/DOE Improved Oil Recovery Symposium, 3-5 April, Tulsa, Oklahoma
- Publication Date
- Document Type
- Conference Paper
- 2000. Society of Petroleum Engineers
- 3 Production and Well Operations, 6.5.2 Water use, produced water discharge and disposal, 5.1.2 Faults and Fracture Characterisation, 5.3.4 Reduction of Residual Oil Saturation, 1.8 Formation Damage, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 5.3.1 Flow in Porous Media, 4.1.2 Separation and Treating, 5.4.1 Waterflooding, 2.4.3 Sand/Solids Control, 5.7.2 Recovery Factors, 4.3.4 Scale, 1.10 Drilling Equipment, 5.1 Reservoir Characterisation, 1.6.9 Coring, Fishing
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This paper introduces a new diverting agent that has been developed to control water production in high salinity, high temperature reservoirs. Several dry gels have been crushed and sieved to obtain different cuts of gel particles. The dry powdered gel particles swell in water to give a stable suspension. The swollen pre-gelled (PG) particles do not dissolve in water and can move inside the porous media. Results presented here include test pilots and laboratory experiments. PG particles have been successfully used in two recent pilot tests in Shengli Oilfield, China. Micromechanisms of particle motion and oil mobilization have been studied through transparent glass micromodels experiments. Core tests have also been conducted to verify the selective placement of the particles. According to the experimental laboratory results we can conclude that the mechanisms responsible for the enhancement of oil production are the following:
After swelling and under a high pressure gradient (near the wellbore), the pre-gel particles can deform to pass through small pore throats, ensuring displacement of the residual oil. When the pressure gradient is too small (away from the wellbore) the particles plug the pore throats changing the flow pattern inside the reservoir.
In addition, as the gelation is accomplished before the injection, the PG particle technique overcomes some of the most important problems which can be encountered by classic gel treatments: lack of control of the gelation time, lack of control of the stability of the gel formed or ungelation due to adsorption, dilution or degradation of the polymer or pH change. Furthermore, due to these specific characteristics, this process can be used in oilfield environment that would prevent the in-situ gelation of a classical gelant solution.
Most of the oilfields in China were discovered in continental sedimentary basins. They are characterized by complex geologic conditions and high permeability contrasts inside reservoirs1. In the absence of active aquifer, these oilfields were developed by water injection at the early stage of their development. However, serious vertical and lateral heterogeneity in formations resulted in a rapid increase in the water-cut of oil wells. To improve oil recovery the study on enhanced oil recovery has been carried out for more than 15 years2,3.
Recently, specific attention has been paid to the gel technology for profile modification treatments of heterogeneous reservoirs.
Three injection techniques (bulk injection4, sequential injection5, and colloidal dispersion gel-CDG6) have been tested with several gel formulations7-9. From these experiments and from the state of the art on gelation systems110-12, it appears that: (1) Bulk injection requires high polymer and high crosslinker concentration and it is therefore often uneconomical to inject large volume of gel to correct in-depth permeability variations. Although great efforts have been made to delay the gelation time of bulk gel to insure in-depth placement, the question of when the gelation occurs in reservoir still awaits answers. (2) The main technical problem with the sequential injection is the limited control of where and when polymer and crosslinker meet to form a gel within the reservoir. Due to adsorption, dispersion, dilution or even degradation of polymer, the control on the strength of the gel formed is also poor. (3) The CDG technology, which can be described as a bulk gel that requires low polymer and crosslinker concentrations, have been used in several oilfields in China, but proved to be inadequate to most of China reservoirs environments where extreme channels exist; the temperature range (<90°C) and salinity range (<5000mg/l) are also too narrow to allow the development of CDG technology in China.
PG particles have been designed to overcome the main drawbacks of others gel injection techniques - lack of control on gel formation, temperature and salinity limitation- while fitting China oilfields characteristics (extreme channels, high permeability streaks). In the PG particles injection, small particles of preformed gel are injected in the porous formation.
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