Contaminated Water Production in Old Oil Fields With Downhole Water separation: Effects of Capillary Pressures and Relative Permeability Hysteresis

Abstract

Industry operators using downhole water separation technology in bottom water drive reservoirs with water coning problem have employed two major approaches. One approach uses downhole hydrocyclone and pumps to separate water from oil in one co-mingled production stream. This approach involves elaborate completion design and high cost equipment. The second approach, termed "gravity segregation" uses dual completion technology with zonal isolation packer to separately produce the water and the oil and so counter the cone development at the wellbore. Both methods, currently, do not completely eliminate the problem of contaminated water production but reduces it to, perhaps, some manageable level. The growing emphasis on environmental-friendly oil production operation and increasing cost of water handling requires the production of oil-free disposable water in a simple completion design. This paper presents case studies of the pre-installation design of gravity segregation method for three fields (West Africa, Gulf Canada and Louisiana) with strong water coning problems. The study confirms that old oil fields that have suffered severe water coning exhibit a transitional saturation profile and dispersed oil-water contact. In addition, the imbibition/drainage process of water cone development and reversal induced by gravity segregation creates relative permeability hysteresis effect. The effects should be included in the pre-installation modeling. The results using numerical simulator, indicate that the combined effects of capillary transition pressures and relative permeability hysteresis are responsible for the production of contaminated water experienced with application of the gravity segregation approach in old oil fields. It also shows how to add an envelope to the well's inflow performance window to accommodate the transition zone. Inside the envelope production of oil-free water from the bottom completion is possible with production of minimal water cut oil at the top. This uncontaminated water could be disposed while operators maximize the use of their pipeline and water separation facilities as well as improve oil recovery.

Loss and restoration of water coning control – field case history and prediction

“…Similar mechanism is employed in the DWS technology for local control of water coning [34]. Generally, a DWS well has two completions: the top completion is installed in the oil pay zone to produce oil, and the bottom completion is placed in the aquifer to keep the oil water contact (OWC) beneath the top completion [35][36][37][38][39][40]. To date, various versions of DWS technique have been developed by the Downhole Water Sink Technology Initiative (DWSTI) research program at the Louisiana State University (LSU) -including Downhole Water Loop (DWL), and Bilateral Water Sink (BWS) etc.…”

Identification of technical barriers and preferred practices for oil production in the Appalachian Basin

“…This problem can be addressed with better water saturation monitoring where real time monitoring and control could be implemented. The detailed description of this technology and guidelines for proper applications are given by Wojtanowicz 17,19 . Also, Davis et al 16 and Plahn et al 18 present some experience from field applications using dual completion method.…”

“…Also, resistivity and porosity logs (sonic, density, neutron) can be combined to determine the location of water and pay zones which later can be compared to cased hole logs to look for coning in producing reservoirs 8,9,10,16,17,19 . Three-dimensional coning is a difficult problem, which can be solved applying a dual completion technique 8,9,16,17,18,19 . The other processes to eliminate or reduce the water-coning problem are to decrease the production rate to shut in the well for several months (around 2 or 3 months).…”