Study On The Mechanism Of CO - Sub - 2 In The Shallow Low Heavy Oil Reservoir

The contents of this paper are from the reservoir development research subject of Chinese Petroleum’s Jidong Oil Field Filiale, the terrestrial shallow layer of Nanpu has entered high water cut development stage, and the natural or artificial water flooding efficiency is low, it is necessary to carry out the tertiary recovery technology research. As the shallow layer in Nanpu have experienced long-term water flooding, the prominent contradictions of interlayer, the producing degree of water flooding and the conventional water flooding efficiency are low, so how to control water and increase oil have become the primary problem to be solved at present.As Nanpu reservoir is shallow layer, formation temperature and pressure are low, and under the formation conditions, oil viscosity is over40mPa·s, it has closed to areas of heavy oil, this paper will study properties of this kind of low heavy oil.This paper will take heavy oil reservoir in G104block in Nanpu of Jidong Oil Field as the research object. For the problem of fast water cut rising and low oil recovery in the middle to late period of the water injection in the low heavy and heavy oil reservoir, carry out the numerical simulation of CO2huff-puff about controlling water cut and increasing oil production though laboratory physical modeling and individual well CO2huff-puff. In order to study CO2huff-puff mechanism and feasibility of water control and oil increase, carry out experiments in laboratory about compatibility of CO2with formation oil/formation water, phase permeability experiment about water flooding/CO2flooding, CO2slim tube experiment, long core experiment and single well numerical simulation about CO2huff-puff to control water and increase oil.The following understandings are obtained through this paper study(1)The compatibility of CO2with formation oil experiment results show that, CO2has capacity of dissolution increase and viscosity reduce on oil., under the low formation temperature and low formation pressure, CO2can be well dissolved in the formation oil to reduce the viscosity of oil, and then achieve the goal of increasing oil.(2)When dissolved CO2formation water flow to the narrow pore, with the pressure reduction, the CO2will precipitate from formation water, create Jamin effect, ultimately achieve water control effect.(3)From CO2slim tube experiment, the minimum miscibility pressure for CO2injection is about26MPa at reservoir temperature, the miscibility pressure is much higher than the current formation pressure15MPa, and higher than the original formation pressure22MPa, miscible flooding development costs, recommend CO2huff and puff development.(4)From long core experiment, exhaustion recovery is only1.9%; after the exhaustion continue flooding recovery is59.9%. after the exhaustion continue flooding to the moisture content of80%, the moisture content change drops by at most25.95percent after CO2huff and puff, recovery efficiency up to65.02%, this indicates that water injection can effectively improve the low recovery factor of low heavy oil reservoir, CO2huff and puff has effect on water control and oil increase. (5)The single well numerical simulation about CO2huff and puff control water and increase oil further validates that CO2huff and puff has effect on reducing the oil viscosity and obvious effect on water control and oil increase.