Fundamentals Of Enhanced Oil And Gas Recovery From Conventional And Unconventional Reservoirs PDF Download

Rapid production decline is typical in oil production from unconventional reservoirs. Enhanced oil recovery (EOR) with gas in cyclical (huff-n-puff) injection mode is arguably the most feasible method to solve the problem of relatively low oil recovery in the low permeability reservoirs, as supported by wealth of evidences. Nonetheless, the results so far seem vary widely. In some cases, the results are encouraging, while in some others, they are marginal. There seems to be many parameters to be considered in predicting the chance of a huff-n-puff gas EOR success. It is of interest not to just be able to forecast whether a huff-n-puff gas EOR will result in a satisfactory result, but also to obtain the highest oil recovery achievable, at least theoretically. With reliable real field data, rather than the synthetic one, research to identify the most significant factors affecting the gas EOR results in unconventional reservoirs by means of the widely used numerical simulation, is possible. The origin of the data should arguably give more credibility to the results, and thus their related analyses. Once the significant factors are identified and how they interact is understood, an optimum operational parameters design that maximizes the oil recovery is attainable. The acquired knowledge can also be of use in reducing the unknowns in other attempts with other methods to improve unconventional reservoirs’ oil recovery, so that the focus can be directed towards the right direction. Admittedly, uncertainties are inherent to the procedures used, but they are assumed to be acceptable for the purpose. This research found that the maximization of the oil recovery from unconventional reservoirs is viable and it is worth the resources spent. There seems to be some kind of matrix permeability threshold, below which the gas EOR will return meager even negative incremental oil recovery. This is because in order for the EOR to work well, the oil phase must be able to traverse with reasonable ease in the matrix, unless the injection gas effectively vaporizes the reservoir oil phase. Good injection gas choices are the ones that lower the oil viscosity while monotonically vaporize it in reservoir conditions. Field gas, [CO2, C2, C3, and C4] are usually good injection gas choices, with certain conditions. Single oil or gas phase in reservoir conditions is desirable, as the presence of another phase will adversely affect the phase flow, as described by the relative permeability curves concept. Good operational parameters are the ones that facilitate the production of the heavy components the most, while minimizing the obstruction to the oil influx from the matrix to the SRV. By extension, it is suggested that the use of water-based surfactant could be detrimental to the oil recovery in the long term, as the water phase will block the injection gas contact with the reservoir fluid. The inability to apply sufficiently high pressure without adversely affecting the aforementioned oil influx is a concerning challenge in the real field EOR implementation. Unless the reservoir permeability is enough to allow adequate oil phase mobility, it may be more reasonable to produce such unconventional reservoirs in primary production mode. Moreover, a higher GOR tends return a higher incremental oil recovery for black and volatile oil, in case of the EOR is applied from the beginning without a preceding primary production period. The data obtained from the oil-producing fields is also used to develop some kind of screening criteria for injection gas type, within which a huff-n-puff gas EOR will result in a good incremental oil recovery. The criteria cover the reservoir pressure, oil viscosity, C7+ molar fraction, and fracture conductivity. However, due to the available data is for reservoir oil with relatively low viscosity, the screening criteria is also more appropriate for such type of reservoir oil. As for the reservoir permeability point of view, the screening criteria is more suited for unconventional reservoirs with permeability of 685 nanodarcy or higher