Scale Management of Production Wells via Inhibitor Application in Supporting Injection Wells

Abstract

At the present time, the YUKOS Oil Company is applying various techniques to maximize oil recovery. Some of these techniques, such as waterflooding, are leading to an increase in the number of wells that face scaling problems. Various technologies are being used for scale management in these wells, including, for example, continuous inhibitor dosing utilising surface dosing systems. This method has some disadvantages, including the high cost of the service. In addition, this technology only protects downhole equipment from damage by scale deposits, but the bottomhole formation zone remains unprotected. Some years ago we recommended that production wells be protected via scale inhibitor application in the injection waters used for reservoir pressure control and sweep. Experiments conducted have shown that this technique may be used for certain production well types with scaling problems when these are located in relatively close proximity to their supporting injection wells. This paper presents the experimental and field results when this technique was tested in the South-Surgut oilfield. Before testing, a preliminary investigation of the formation geology and hydrodynamic connectivity between injection and production wells was carried out. Next, a large number of experiments were carried out to select an efficient inhibitor chemistry, to test for inhibitor adsorption on the reservoir rock, to evaluate an initial MIC for the solution, and to determine the inhibitor dosing periodicity. During testing of this technique, the inhibitor concentration in the produced water was regularly measured, and the impact on protection against scale was continuously evaluated. It was demonstrated that the inhibitor concentration in the produced water did not decrease below 5–10 ppm on average during 150–200 days for all wells. As a result, the interval between workovers for pump equipment increased by approximately 2.5 times. Furthermore, oil production was increased relative to the period before introduction of this technology. An economic evaluation was carried out that showed the viability of using this technology for the protection of wells in a compact injector-producer pattern. Introduction Due to application of various techniques to maximize oil recovery in Yukos oilfields, the number of wells with scale problems is increasing. As the results of analysis of deposits on ESP wheels shows [1], the portion of inorganic deposits which is soluble in hydrochloric acid amounts to 99.8 % [2]. In addition, it should be mentioned that the content of the iron oxides and hydroxides are low in comparison with calcite and magnesium carbonate deposits. As is well known, the main reasons for the formation of carbonate deposits are pressure and temperature changes during oil production [3–6]. These may lead to decreasing carbonic acid content in the produced fluid and, as a consequence, to carbonate scale depostion on downhole equipment:Equation 1 The main scale prevention methods in Western Siberian oilfields are as follows [7]:A continuous dosing either topside or downhole.A periodical inhibitor dosing at the well bottom hole.Inhibitor treatment application via pressure support water injection wells. For scale prevention the continuous inhibitor dosing utilising surface dosing systems is widely used [3]. In spite of its efficiency, this technology has disadvantages, such as high costs for dosing and system maintenance. An alternative to this technology is inhibitor dosing into the injection system. The first experiments using this alternative technology were carried out in Bashkortostan, but without detailed analysis of the results. Yukos Oil Company is interested in trying this new method elsewhere, and the South-Surgut oilfield (Khanty-Mansi Autonomous Area) was selected for testing.

Investigation of the Asphaltene Inhibitor Effect On reduction of the Scaling Intensity in Formation and Wells

“…К основным причинам образования солей в нефтяных скважинах при разработке месторождений относятся [1][2][3][4] Уровень инженерного сопровождения в МС обеспечивается следующими данными.…”

The Problem of Scaling and Ways to Solve it in the Oilfields of Rosneft Oil Co.

“…To predict scaling potential, intensity of scaling in wells and pump equipment, a simulation study has been run to model the change of salt saturation of produced water [3,4]. Software SPOW [5] based on J.E.Odd, M.B.…”

“…Thus, OAO "Yuganskneftegas" water belongs either to hydrocarbonate or calcium chloride type with the salinity of 6,4 -47,8 g/l and the following content of salt-forming ions, mg/l: Са 2+ = 22,6 -473, SO 4 2-= 0 -161, НСО 3 -= 195 -2640. Produced water of Rosneft-Stavropolneftegas belongs to the calcium chloride type.…”

“…Produced water of Rosneft-Stavropolneftegas belongs to the calcium chloride type. Its salinity varies from 35,4 to 139,1 g/l and salt-forming ion content varies within the following limits, mg/l: Са 2+ = 304 -16514, Ва 2+ = 12 -875, Sr 2+ = 67 -962, SO 4 2-= 0 -463, НСО 3 -= 183 -915. Water of Rosneft-Purneftegas fields mainly belongs to the calcium chloride type.…”

“…As adsorption process prevails over chemical desorption from the reservoir rock at the initial stage of inhibitor injection along with the injection of water into the reservoir pressure maintenance system, then, at the first stage the injection of shock doses of the inhibitor is carried out for 10 days with a frequency of one injection every other day. Then, for 20 days an optimum dose of the inhibitor is injected every other day [4].…”