Particularity Analysis Of Solution Gas Drive In Tight Oil Reservoir

Tight oil reservoir as a kind of unconventional resources is a newly discovered resource in recent years.The development of tight oil in the United States changed American decline trend of oil rate,It makes the production has entered into the phase of rapid growth.Previous studies of the Bakken tight oil reservoir found when the reservoir entering two-phase flow,there's a tendency to increase of Estimated Ultimate Recovery.This is completely different with the research about rate reduce in the stage of solution gas drive reservoir(or IPR curve deviates from the straight line begins to be convex).It is still not sure this statistical result is just an accident,or it is may be a kind of special phenomenon in the solution gas drive of tight oil reservoir.This is also the research contents of this article to continue.This paper combined the information of this special phenomenon in Bakken Bicentennial area with some calculation methods to calculate and statistics.The results are consistent with the previous studies that when the estimated ultimate recovery is increased in solution gas drive reservoir enter the two-phase flow,and confirmed this special phenomenon in Bakken tight oil reservoir.In order to study this phenomenon,this paper analyze the influence factors of this particularity through to the process of tight oil reservoir production decline types and reservoir properties and fluid properties.Decline types is mainly through the theoretical formula of the approach for the analysis of reservoir parameters in different produced stages.The first stage is the reservoir pressure above the bubble point pressure.This paper estimate the reservoir properties by the matching of Fetkovich/Mccray classical curves and production date;the second stage is the reservoir pressure blow the bubble point pressure.In this stage,the reservoir properties estimated by a new method which is calculate the reservoir properties in two-phase flow phase under the different permeabilities.This paper simulate the three types of gas oil ratio in Bicentennial through the numerical modeling,and studied the reservoir properties and fluid properties of scatter,constant,constant to rise of gas oil ratio.Compared with the changes of the period of solution gas drive beginning found that the second stage the estimated initial oil in place is higher than the first stage,also the most of permeabilities of second stage is higher than the first stage.By comparing the production data under the condition of high permeability and low permeability found that the permeability which by the production calculated appeared on convex in a short time when the solution gas drive beginning at the high permeability condition,then the permeability declined rapidly and even though it is lower than before the solution gas drive.It is improved that the normal condition.Under the condition of low permeability or ultra-low permeability reservoir modeling appeared on the convex phenomenon also,but this phenomenon appeared for a long time,especially in the process of permeability decline.During this period no matter the estimated initial oil in place or the ultimate recovery are all higher than before the saturation gas drive.This may be one of the reasons lead to abnormal phenomenon.The results of numerical simulation analysis: Unstable oil well produced lead to scattered production gas oil ratio.Various parameters have the similar situation under the condition of gas-oil ratio constant and constant to rise.The smaller the permeability,gas-oil ratio rises the slower;On the contrary,the more rapidly the gas-oil ratio rises;the smaller the porosity,the more rapidly the gas-oil ratio rises,and vice gas-oil ratio rise more slowly;The lower the viscosity of gas-oil ratio rises faster,conversely the more slowly.These changes are the same with conventional reservoirs.A certain period of time after the solution gas drive gas-oil ratio change anomalies.When the viscosity is less than 1 mPa·s,gas-oil ratio showed a trend of sharp rise,after a period of time the changes tend to be normal.This may be the influence factors of affect the solution gas drive in tight oil one of the reasons.In general,in tight oil reservoir,due to its low permeability characteristics of solution gas drive appear within a period of time after the viscosity resistance increase,oil phase permeability to gas and free gas driving force increases,the tradeoffs between effects the solution gas drive reservoir recovery efficiency.