Intensive Reservoir Injection CO 2 Experimental Study

With the increasing demand for oil resources and the decreasing of conventional oil and gas, the great potential of tight oil is becoming the new highlight of global petroleum exploration. Facing the low production and low benefit, enhancing oil recovery is one of the important technology to promote the development of tight oil. Among the various methods, gas （CO₂） injection has the unique mechanism and advantages of reducing viscosity, swelling and miscible flooding. But, there is a lack of research in key controlling factors and mechanism, interaction of CO₂ and minerals and effect miscible mechanism in tight reservoir, etc. This research is on the basis of the National Major Fundamental Research and Development Project "The mechanism and method research of enhancing tight oil recovery" （NO.2015CB250904）, based on the literature research about gas injection in tight reservoir, a series of CO₂ injection experiments were carried for the JM tight reservoir. First, reservoir cores and fluids were analyzed, and the study of high-pressure physical property of formation fluids and CO₂ injection swelling test was carried out. Then, the minimum miscible pressure of formation oil and CO₂ was tested by slim tube experiment. Finally, conducted the CO₂ injection experiments under tight condition, which contained huff-puff, replacement and flooding nuclear magnetic resonance experiments. The above experiments results pointed:（1） The tight cores have the characteristics of tight overall, rough surface, no natural fracture and few intergranular holes. Formation water salinity was 29776.2mg/l and the pH was 8.9. The tight oil has a low viscosity and highly affected by temperature.（2） The crude oil properties was becoming better with the increasing of CO₂ injection rate, and there was an increase in saturation pressure and volume factor, a decrease in viscosity and density gradually. The slim tube test showed the minimum miscible pressure of formation oil and CO₂ was 17.2MPa.（3） Recovery degree was higher when pressure increased, but the CO₂ consumption raised accordingly. During a certain range, the final recovery degree of CO₂ soak increased with the decreasing of crude oil, the rising of soak time and production pressure differential.（4） Equal molecular replacement had a certain oil displacement contribution during CO₂ injection in tight condition.（5） Under immiscible pressure, there was a poor contact on CO₂ and formation oil, displacement was showed as two phase flow, it had an early gas breakthrough and a low recovery degree, the produced oil mainly came from the large channels. For the miscible pressure flooding, it showed a certain miscible effect and had a later gas breakthrough, oil both in small and large channels were displaced well and brought a homogeneous displacement and a high recovery degree. Besides, CO₂ would lead to the colloid and asphaltene of oil deposition in pores.Through the relevant experimental study of tight oil CO₂ injection, it could provide some theory reference on the ideas and methods for the efficient development of tight oil.