At the initial state, some oil reservoirs have zero percent water cut at initial water saturation. This condition is an indication of zero water relative permeability. The water cut increases gradually until the economic limit of oil production is reached and the well is shut-in. A thorough analysis of recovery from individual wells is required to determine whether the oil still remains in the fluid path and the possibility of the existing pocket oil in unconnected rock pores. Some oil reservoir or formation has an affinity for oil. At the initial state of the reservoir of formation, the pressure is still high, in which the pressure is capable of moving oil into the wellbore. In the depletion period, the pressure is decreasing over time until sometime the pressure is not strong enough to drag oil which is stuck on the rock pores into the wellbore. In this period, a newly drilled well tends to have a low influx since even the water is plugged by the stuck oil.
Let’s assume we have a hypothetical well with properties as of in Figure 1. The well had produced 137 MSTBO. The production rate vs. cumulative time is plotted on log-log type-curve paper. The matched points are retrieved from the type curve and the drainage radius is obtained which is 6200 ft. The volume of oil influenced by the well is 30 MMSTBO. The recovery is only 3%. The oil company has a good opportunity to increase production since the well has high recoverable oil reserves remain. Unfortunately, the oil has a mobility problem and the reservoir drive is not capable to move the oil into the wellbore.
Some well stimulation companies are actively researching to improve oil mobility and decrease the pressure required to move the oil into the wellbore. The imbibition well stimulation is mainly to increase the oil mobility by injecting chemical products into the reservoir. Since every crude oil has unique properties than an imbibition laboratory test utilizing capillary tube tests with several chemical products is conducted to find the suitable chemical products.
In the case of above well which has low oil recovery, the core from the well is saturated with reservoir fluid and imbibed by formation water or brine. The oil recovery is only 3.9% or slightly higher than the current recovery. The same core is then imbibed by several ionic or nonionic surfactants. One of the surfactants can recover 26% of oil. If the surfactant is applied in the field, we can expect the well producing another 7.663 MMSTBO. We can positively conclude that the well has a huge oil potential left in the fluid flow path.
In the present invention of William Weiss, several field applications are suggested since there are a large number of variables involved. From those field applications, we will get several set variables. Those sets of variables are then inputted into Neural Network which will correlate all variables. Fuzzy logic neural networks are used as analytical tools throughout the Neural Network. The output will be used to forecast the production and to determine the surfactant usages.