Production Optimization & Enhanced Oil Recovery

(Introduction to New Technology)

Applicability and Key Benefits

The proposed innovative technology for Oil Production Optimization & Enhanced Oil Recovery (further in the text it's referred as TPO - Technology for Production Optimization) is primarily applied for optimization of oil production from reservoirs containing oil with high Gas to Oil Ratio (GOR>600 cft/bar). It is used when bottomhole pressure is below bubble point pressure (P_bottom<P_bubble_pt) and/or in case when a gas cone appears. TPO can be applied to all methods of oil production - fountain, gas lift, and pump production. This technology is based on a very precise mathematical model of the system "reservoir-well" and all of its components.

It allows maximization of the current oil production rate and enhancing oil recovery by keeping current bottomhole pressure on the "optimal level".A principal novelty of the proposed technology is that that the maximum oil flow rate is reached at a certain value of downhole pressure between zero and formation pressure, called "optimal", or P_opt. The fact that such an optimal pressure value exists has been proven both theoretically by running extensive modeling and practically by conducting several field experiments. This optimal pressure depends on formation parameters (permeability, porosity, saturation, and pressure), PVT ( R_s(P,T) - solution of gas in oil; B_o(P,T) - oil formation volume factor; B_g(P,T) - gas formation volume factor; mu_o(P,T) - oil viscosity; mu_g(P,T) - gas viscosity) characteristics of fluids, and other characteristics of the entire system "Well - Formation".

Maximum oil rate is achieved by maintaining formation in the mode that minimizes negative effects in the bottomhole area. These detrimental effects appear due to the presence of a free gas separated from oil that blocks oil flow, as well as due to forming of zones of sluggish, viscous degassed oil. Utilization of this method also decelerates pressure drop in formation by lessening premature gassing from formation; it also decreases a current value of GOR. This leads to extended life and increases ultimate production index of a particular well.

The proposed mathematical models allow accurate calculation of optimal conditions for existing parameters of the formation and the system to reach maximum oil production. In addition to determination of P_opt , these mathematical models and corresponding computer simulators allow determination of other parameters of the most optimal mode (e.g., optimal rate of injection, power of pumps, etc), calculation of critical design parameters of both surface and downhole tools (see below) used for implementation of this technology, and expected oil production improvement. Also, these high precision simulators allow diagnosis of current well conditions and prediction of its behavior in the future, including oil production rate, pressure, GOR, and the recovery index.

This technology can be relatively easily implemented by using a Downhole Tool (DHT) for adaptive regulation of downhole pressure during production. This tool will automatically keep this pressure closely to the optimal level P_opt. in various production conditions.

Besides the obvious key benefit, i.e. increase in oil production rate, the proposed technology brings numerous additional benefits, such as the following:

Reduce the current GOR and WOR

Reduce gas and water cones

Decelerate depletion of formation pressure

Increase ultimate recovery index of the well and the oil field

Eliminate gas and water cones

Improve stability of well performance

Avoid premature loss of formation pressure and energy

Increase life-time of wells

Eliminate appearance of high viscosity areas in formation near bottom hole zone

Increase formation’s relative permeability coefficient by oil

Increase productivity index of the formation

Increase in the efficiency of gas-lift and pumps

Decrease in electric energy consumed by pumps and gas-lift compressors

Reduce formation sand washout, mechanical damages to the formation, and formation permeability loss

Examples of practical utilization of TPO - Field Test Results

A field experiment was conducted at an offshore gas-lift well located in Gulf of Mexico. Changes in main parameters of well production for three observation intervals (specifically - before installation of TPO tool, during presence of TPO tool downhole, and after its removal) were closely monitored and then analyzed.

Here is a summary of main results achieved at that well due to utilization of TPO:

oil flow rates increased by 35%;

wellhead pressure increased by 50%;

water cut reduced from 28% to 22%;

GOR decreased by about 66%;

gas injection decreased by 50%.

An interesting effect resulting in oil flow rate increase and production of additional 7760 barrels of oil was observed after removal of the TPO tool. It can be explained by the rejuvenation of the near-the-bottom formation zone during usage of a downhole TPO tool. This is another positive effect of TPO that achieves results that are similar to other oil production intensification techniques (e.g., hydro-fracturing or acid treatment).

Another successful field test was conducted in Uzbekistan in 2001. Utilization of TPO at that well yielded the following positive results:

daily oil production was up from 780 to 920 bpd (+18%),

GOR went down from 6000 to 4500 scf/bbl (-15%)

water cut has fallen to zero and stayed there.

These results were achieved by installing a downhole TPO tool in the tubing. That generated additional variable hydrodynamic drag, which automatically maintained an optimal bottomhole pressure and stabilized the well's performance. This allowed us to reduce the skin effect in the bottomhole zone and to eliminate gas and water cones from perforations. The use of the TPO at that well yielded approximately 37,500 barrels of additional oil over a nine-month period.

Economic Effectiveness of TPO

The Economic Effectiveness of the TPO is achieved due to the combination of all benefits listed above. Overall, it is related to the improved conditions for oil production. The number of wells suitable for potentially beneficial employment of TPO is really huge. This technology can be utilized for all oil production techniques, i.e. fountain, gas-lift, pump, etc.

The method can be applied both during development of new oil fields and for improvement of older wells. The economic effect from implementation of this technology can be expressed in terms of getting millions of additional barrels of oil without drilling extra wells or building additional expensive platforms for offshore production.

Simulation of Negative Effects in Near-Bottomhole Zone

Results of computer simulation: Rate, Formation Pressure and GOR vs. Oil Recovery

Initially this well was working in a non-optimal mode (P_bot ≠ P_opt); then it was switched to an optimal mode when P_bot was maintained closely to the optimal value P_opt