Case Study: High-Energy Elastic-Wave-Based EOR Crosses Flow Barriers in a Canyon Sand To Reverse Oil Decline

Abstract

_ Over the past several decades, engineers and researchers have continually explored ways to release valuable and significant quantities of oil left behind by primary and secondary production methods. Many flow-based enhanced oil recovery (EOR) methods have long been proven to work well in connected formations, where a fluid can communicate between injection and production wells. But in fields characterized by isolated, noncontiguous reservoirs, flow-based EOR methods cannot work. Conventional stimulation methods such as acidization, because they treat only one well at a time, are inefficient, time consuming, and uneconomic for fieldwide production enhancement. The use of high-energy elastic-wave-based EOR overcomes these communication issues. Elastic waves propagate powerfully through rock and fluids to effectively enhance oil recovery in formations located both vertically and horizontally within about a 1.5-mile radius of the source well. The following case study demonstrates the issue, the process, and the result of a typical course of action. The Issue With rapidly declining production in a southwest Texas’ canyon sand, a producer was facing the reality that its field would play out in about 2 years, at which point it would have to be shut in. Over the field’s 70-plus years of production, its historic decline rate was about 46% and the average well was eking out just 3 B/D. The producer understood that water or CO2 floods were out of the question due to the isolation of each well’s sand lens. Having heard about elastic-wave EOR’s ability to traverse those barriers, the company asked Zencor Tools to field-test its procedure. This would determine whether the field could return to productivity or would have to undergo a hugely expensive shut-in process. At that point, Zencor had yet to test its results in these types of vertically and horizontally isolated reservoir systems and were greatly interested in performing a case study (Fig. 1). Test Preparation The installation of an elastic-wave EOR tool starts by selecting an abandoned well that is centrally located to the most-dense production area. An elastic-wave EOR tool is placed to provide the greatest enhancement to oil recovery and extension of field lifespan. For the canyon sand test, the selected well brought about effective EOR in the 70 wells that were part of the treatment process (Fig. 2). Tool Installation Before installing the tool, the abandoned well must be cleaned out and a short, 50-ft cement plug placed above the perforations. The cement plug prevents formation gas from entering the wellbore and interfering with the tool’s performance. The tool is then run into the well on tubing; sucker rods then follow with the polish rod spaced and connected to a surface pumping unit. The pumping unit is then started to begin EOR. No maintenance is required other than lubrication of the stuffing box. For this test, the depth was set at 3,500 ft, and while there is no physical limit on depth other than rod string length, it can generally be effective down to 8,000 ft.