A Mechanistic Model Based Approach to Evaluate Oil/Water Slip at Horizontal or Highly-Deviated Wells

Realizado por GRAJEDA LEN Amy WindA Mechanistic Model Based Approach to Evaluate Oil/Water Slip at Horizontal or Highly-Deviated Wells

AbstractSlip velocity between phases is an important factor in interpreting production logging survey, however, no much work has been done for determining the slip velocity when oil and water flow simultaneously in a horizontal or highly-deviated well.

There are several correlations and models that may be used to determine the slip velocity, nevertheless, they were developed for vertical wells and can not be applied for horizontal or highly-deviated wells due to the different mechanisms dominating the fluid flow.

IntroductionExcessive water production is a common problem necessary to be taken care of by many oilfield engineers. For improving the production of a problem well and for general reservoir management purposes, it is crucial to determine the location and amount of water entries in a specific well. Production logging is normally served for this purpose.

Horizontal and multilateral wells have become the standard practice in the oil industry. Oil and water flow in a horizontal or highly-deviated well is quite different from that in a vertical well. For example, gravity plays a very important role for oil and water flow in a vertical or slightly deviated well. Because oil is usually lighter than water, oil tends to move faster than water for upward flow, but slower for downward flow. This is not true for oil and water flow in a horizontal or highly-deviated well.IntroductionFor oil and water flow in a horizontal well, many different flow patterns have been observed. These flow patterns may be classified into two categories: segregated flow and dispersed flow.

Six typical flow patterns observed in horizontal pipes are listed as follows:

Stratified flow (ST)

Stratified flow with mixing at the interface (ST & MI)

Dispersion of oil in water and water (D/o w & w)

Oil in water emulsion (O/w)

Dispersion of water in oil and oil in water (Dw/o & Do/w)

Water in oil emulsion (W/o)

IntroductionAs a rule of thumb, the first three flow patterns can be considered as segregated flow, while the last three can be approximately handled as dispersed flow. Flow characteristics are different in different flow patterns.

Unfortunately, it is not easy to accurately measure or determine slip velocity. A mechanistic model based approach to evaluate the slip between oil and water phases is presented in this paper.

Marco TericoFlow RegimeA description of the geometrical distributionof multiphase fluidmoving through a pipe.

For oil-water mixtures, the most common regimes are bubble flow, slug flow and emulsionflow. In horizontal wells, there may be stratified or wavy stratified flow in addition to many of the regimes observed in vertical wells.Marco TericoSlip VelocityThe difference between the average velocities of two different fluids flowing together in a pipe.

In vertical ascending flow, the lighter fluid flows faster than the heavier fluid. The slip velocitydepends mainly on the difference in density between the two fluids, and their holdups.Marco TericoHoldupWith reference to multiphase flow in pipes, the fraction of a particular fluid present in an interval of pipe.

In multiphase flow, each fluid moves at a different speed due to different gravitational forces and other factors, with the heavier phase moving slower, or being more held up, than the lighter phase.

The holdup of a particular fluid is not the same as the proportion of the total flow rate due to that fluid, also known as its cut.

To determine in-situflow rates, it is necessary to measure the holdup and velocityof each fluid. The sum of the holdups of the fluids present is unity. The holdup ratio is the ratio of the holdups of two fluids, and is sometimes used as a parameterto express the phenomenon.Mechanistic Approach to Determine Liquid HoldupEven with identical water cut, the in-situ water fraction (water holdup) can be very different dependent on the flow pattern existing in a pipe. Correct determination of flow pattern is thus an important key for accurate prediction of water holdup. In the present paper, a mechanistic model based approach is applied to determine the water holdup.Mechanistic Approach to Determine Slip VelocitySimilar to the in-situ water fraction or water holdup, slip between oil and water phases is also primarily dependent on flow pattern. It is expected that slip velocity can be large for segregated flow, whereas it should be trivial for well-mixed/dispersed flow.

Pipe inclination plays a significant role in the oil-water slip velocity. As we know, slip is almost always positive (i.e., oil moves faster than water) for oil-water production in vertical wells. This is not true anymore for horizontal or highly-deviated wells. For oil-water flow in horizontal wells, both positive and negative slip can be expected. For upward flow, water phase is generally heavier than oil, hence, oil tends to move faster than water and slip velocity can be positive. In contrast, for oil and water downward flow, water tends to move faster than oil due to gravity and negative slip is anticipated.

A flow pattern-based approach is also applied in our determination of slip velocity. Again, flow pattern is first identified, following by the calculation of slip. Potential ApplicationThe new approach presented in this paper may be applied to evaluate in-situ gas and liquid flow rates using the measured in-situ mixture flow rate and liquid holdup. Summary and ConclusionExisting correlations can not predict reasonable results of oil-water slip velocity for horizontal or highly-deviated wells.

Impact of different parameters for oil-water slip in horizontal or highly-deviated wells is strongly interrelated.

Always try to investigate the influence of all the parameters simultaneously. This can be achieved by using a mechanistic model based approach, such as the one described in this paper.

It is highly recommended that more research be pursued to investigate oil and water flow in horizontal wells.

Focus should be set on the determination of water holdup and slip between phases.

Both theoretical and experimental work should be further conducted.