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Study On Technique And Mechanism Of In-depth Profile Modification For Improving Water-flooding In Offshore Oilfields

Posted on:2007-12-22Degree:DoctorType:Dissertation
Country:ChinaCandidate:X F TangFull Text:PDF
GTID:1101360182480138Subject:Mineral prospecting and exploration
Abstract/Summary:PDF Full Text Request
The technology of in-depth profile modification has been widely used to improve water-flooding performance of onshore oilfields with high heterogeneity and most of its applications succeed. Compared with onshore oilfields, almost no in-depth profile modification has been conducted on offshore oilfields in China before this study. Many offshore oilfields in China have very high heterogeneity in formations and their water-flooding performance is bad. Therefore, it is important to conduct in-depth profile modification on these oilfields, too. However, offshore oilfields have their own production conditions and completion method. So, the study of profile modification on offshore oilfields is necessary.The study, part of in-depth profile modification technology to improve recovery for Bohai oilfields, is supplied by 863 program. Firstly, a fully investigation of lately technology at home and abroad was done. It is found that the present technology can't be applied to Bohai oilfields for the reasons of their specific reservoir characters and production conditions. New cross-linked weak polymer gel with the ability of fast gelation which meets the requirements of Bohai oilfield is put forward and studied. Secondly, it is well known that under the mode of "gelation after injection", the quality of the gel can't be guaranteed. Furthermore, the aim of in-depth placement can't be effectively achieved. A new mode of in-depth profile modification, named "gelation while injecting", is put forward in the thesis. Indoors tests of long sand-packed cores with automatic pressure survey system have been done to study its corresponding mechanism. It is found that the mode of "gelation while injecting" fits pay zones with high permeability streaks only. Thirdly, the technology was applied to in-depth profile modification field test on Bohai offshore oilfields. Oil production of offset wells distinctly increased and economically effectiveness was obtained. Creativities of this paper are illustrated as follows:(1) A new cross-linked weak polymer gel which is characterized by salt-resistance and good solubility was developed. It is the first kind of profile modification agent which fits offshore oilfields with gravel-packed completion. The agent can dissolve quickly in water and then partly cross-link instantaneously to form weak gel. For this reason, bad factors, which exist in delayed cross-linking of common profile modification agent, can be avoided.(2) A new mode of in-depth profile modification, "gelation while injecting", is put forward. Under this mode, chemical agents, which include polymer, cross-linker, etc, are allowed to partly cross-link near well-bore to create weak gel. Contrary to this, it was previously thought that profile modification agents must have the character of delayed cross-linking and only in this way, in-depth fluid diversion can been achieved. The study is the thesis completely change thisthought.(3) Indoors tests of long sand-packed cores have been done to study the flow mechanism of weak gel in porous media. Pressure data and gel property along the long sand-packed core have been surveyed in the tests. It is concluded from the experimental results that the weak gel exhibits two kinds of flow character during the process of injection. At first, filter cake forms on the inlet surface of sand-packed cores, which leads to blockage of the cores. After shearing into pieces and shaping, the gel enters the cores. Then, under the pressure difference, it flows to in-depth formation to produce resistance. Because of this resistance, the flowing direction of injecting water is diverted at far-well-bore. Sweep efficiency of water flooding increases and then a higher oil recovery can be achieved.(4) Operational techniques corresponding to the new cross-linked weak polymer gel have been developed. Its field application shows that the operational techniques and equipments fully meet the requirements of the specific conditions of offshore platforms. Large-scale injection operation on offshore platforms can be conducted.(5)The technology was piloted in SZ36-1 oilfield and Jinzhou9-3 oilfield. History data of production shows that economically efficient results were obtained in the two oilfields. Cumulative quantity of incremental oil exceeded 8.2x104 cubic meters and economic benefit was RMB1.254xlO8. And average input-output ratio was 1:10.11.
Keywords/Search Tags:offshore oilfields, in-depth profile modification, cross-linked weak polymer gel, mechanism of profile modification, field test
PDF Full Text Request
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