New Technology of Optimization of Production of Liquid Hydrocarbons From Reservoirs Containing Oil or Condensate with High GOR and Oil Fringes of the Gas Formations
Authors: Tseytlin S. , Tseytlin D. , Makarian T. , Petrossov V. 
Published: October 2016

Over the last 10 years, a new technology has been developed and successfully tested for optimizing production for oil fields with high gas to oil ratio, (GOR), which we will now refer to as TOP (Technology for the Optimization of Production). Both in theory and in practice, we have demonstrated that oil reservoirs with high GOR have a pressure flow rate relationship (IPR) with a clear maximum level. For example, the bottom hole pressure is clearly defined and provides the maximum open flow production on the reservoir. The consequential decline in bottom hole pressure results in decreased oil production, while the gas cut of the produced oil grows. This may be caused by either the gas skin-effect in the bottom-hole area of the reservoir, or the formation of gas coning. Both of these factors result in a decline in production as the bottom hole pressure drops. Basically, as the GOR and water content of the reservoir increases, so the reservoir production declines. Moreover, it was demonstrated that when the bottom pressure drop is below a certain optimal value, conditions emerge under which the well becomes unstable and gas mode occur [2]. This can explain the difficulties that take place with the production of oil and gas condensate from layers of gas fields that contain oil with a high gas factor. Our interpretation of this phenomenon is as follows.

When you create a difference in pressure and arrive at a certain bottom hole pressure value, let’s call it the optimum pressure, gas coning moves up to the casing perforations. As this process takes place, the gas concentration within tubing the fluid starts increasing while the bottom hole pressure decreases more and more, contributing to increased gas coning and a further drop in bottom hole pressure. In other words, positive feedback is taking place here. This ultimately leads to the oil being driven back from the casing perforations and shifting of the well into gas mode.

Our technology makes it possible, with the use of a special bottom-hole device, to diminish the positive feedback, and, while maintaining bottom-hole pressure at certain optimal levels, to prevent the phenomenon described above. On the other hand, the TOP technology makes it possible to increase the condensate flow rate and productive capacity of gas condensate fields.

It is well known that as gas condensate fields are developed, its bottom hole pressure drops. Because of this fact, due to its retrograde behavior, it starts liquating. This process takes place, most intensively, at the bottom of the formation, which is normally lower than the pressure of the formation itself. As a result of this, skin effect takes place in the bottom of formation. In other words, there is an accumulation of liquid condensate which prevents gas from leaving the formation and, accordingly, well production decreases and there is a danger that this can lead to complete well shut off. It should be noted that the pressure flow rate relationship (IPR) of such a formation has the same form as the above mentioned case, although it is worth noting that the physics of this phenomenon is quite different. Therefore, a certain critical value of bottom hole pressure exists when any further drawdown leads to a condensate dropout into the liquid phase of the bottom-hole formation zone and to a decline of the condensate flow rate. When determining, with the use of specially made simulators, the critical value of the bottom-hole pressure at which such phenomenon occurs, we build up bottom-hole pressure and maintain it in such a manner that leads to the reversed inversion of the condensate from its liquid state into the gaseous one. In this regard, the bottom-hole formation zone gets unblocked and the gas condensate flow rate goes up. (See. Fig.5, where the results of the run tests are presented). We should note that the GOR of the produced oil gets noticeably lower, while the condensate production rate gets higher.

A specially designed bottom-hole assembly (BHA) enables more flexible regulation and automatic maintenance of the bottom-hole pressure to the desired level in order to prevent the dropout of condensate from the bottom-hole zone into its liquid state, and therefore preventing a severe decrease in well performance. The BHA also serves to stabilize well performance.

The test of the TOP took place at two gas condensate wells in Uzbekistan in 2014, both of which proved the efficiency of the technology. The rate of condensate flow increased by over 200% following the installation of specially designed BHAs.