Inclined Gravity Downhole Oil-Water Separator: Using Laboratory Experimental Results for Predicting the Impact of Its Application in High Rate Production Wells

Abstract

As an oilfield goes mature, an increased water cut can significantly decrease the maximum fluid production rate or even stop the production entirely. Therefore, separating produced water from the wellstream as early as possible is a potential way to maximize oil production. A novel inclined gravity downhole oil-water separator concept has been introduced and patented by ABB Research Ltd., which combines gravitational separation with distributed water tapping along the incline separator tube. The concept depicts that the downhole separator can be installed somewhere above the production packer and below SCSSV (surface-controlled subsurface safety valve). Gravitational forces create a separated water or water rich layer at the lower side of the pipe. This segregated water rich layer is drained using distributed tapping points along the separation tube and then flow to surface via annulus, whilst the oil rich layer flow through the tubing continue up to surface. Several experimental tests have been performed and this paper describes how to use the experimental results into a well performance simulator to predict how the inclined gravity downhole oil-water separator modifies the performance of high production rate wells. The study includes the well performance effect of separator setting depth, setting inclination, tubing size and tubing configuration. Well performance sensitivity due to water cut and separation efficiency is also discussed. The simulation results show that inclined downhole oil-water separation is very beneficial and able to increase oil production up to 82% for the selected wells with 81–87% water cut. Introduction Conventionally, oil and water are separated at the surface using gravity-driven separators, where the size of the separator is a function of flow rate and the required retention time. The gravity separators often occupy large portions of the space on the offshore platform. In the mid 80's hydrocyclones and centrifuges have been introduced to treat produced water before disposal. Around the 90's, tests of separation facilities with hydrocyclones as a bulk separator has been carried out successfully. These technologies have directed the industry towards the size reduction of separation facilities at surface. However, a major further step is to separate the bulk of the water in a downhole in-line arrangement 15. Applying downhole oil-water separation (hereafter, called as DOWS) could de-bottleneck the production plant on platform and reduce the space on board, eliminate future need of new constructions to increase water handling capacity. By separating water in the downhole, the liquid density of the wellstream and the back pressure on the formation are reduced. Hence, increasing the drawdown pressure which enhances production (Fig. 1). Three basic types of downhole oil water separator have been classified based on the separation system utilized6. The first type using hydrocyclones, the second based on gravity forces and the third type using membrane separation technology, which is yet to be developed and applied in the field but has been investigated through simulation studies. A new concept in the gravity type separation is inclined gravity downhole oil-water separator with distributed water tapping where the drained water can be controlled effectively. Some advantages of this type of downhole separator are its simplicity, robustness in structure and the little sensitivity to the accuracy of installation angle. Due to its simplicity components, it also has a long-life potential. In the case where the separator fails to perform well it can be kept and used as ordinary tubing without the need of workover cost to pull it out. Some of the challenges to this concept are the design of the instrumentation that can regulate the drainage rate to achieve the best separation and the potential well integrity issue with regards to flowing HC in the A-annulus.

Separation dynamics of immiscible liquids

“…The viscosity is changed by using different oil volume fractions, as seen in Eqs. (10) and (11). The correlation development of Π 1 as a function of the Re is shown in Fig.…”

“…Fitnawan et al [10] investigated the inclined gravity downhole oil-water separator. Based on their study, this separator type has several advantages, including longlife potential due to the simplicity of its components and its robust structure.…”

Numerical simulation and experimental study of two-phase flow in downhole spiral gas-liquid separator

“…Gas-liquid separation technology is important to ensure the safe and efficient operation of industrial equipment so it plays a significant role in many fields (Liu et al, 2020). Gas-liquid separation devices can be divided into two categories: one is gravity settlement (Fitnawan et al, 2009;Lopez et al, 2019), the density difference between the gas phase and the liquid phase is used to achieve the gravity separation. But gravity settlement requires a large settlement space and a long settlement time, so it is not suitable for spaces with limited underground structures; the other is to use the different centrifugal forces generated by rotation to achieve phase separation.…”