Silicon Containing Scale Forming Characteristics and How Scaling Impacts Sucker Rod Pump in ASP Flooding

Abstract

ASP (alkali-surfactant-polymer) flooding improves recovery rate dramatically. However, scaling problem happens in artificial lift systems and causes pump sticking in sucker rod pumps and the average pump running time decrease from 500 days to 37 days. By analyzing the constituents and characteristics of scales from ASP production wells and experimenting with simulating produced liquid, characteristics and mechanism of silicon containing scale forming are researched. The results show that Ca2+, Mg2+, Al3+, polyacrylamide, surfactant and silicon influence the ASP scales structures and forming processes. The ASP scales have the characteristics of absorbing and sticking. Basing on describing of scaling characteristics, mechanisms and the pump structures, the reasons for pump sticking are analyzed. Pump sticking which caused by scaling between the plunger and barrel occurs when the sucker rod pump is sucking, hot water is circulating or the pump is stopping. When the well is shut down, one major reason of pump sticking is scale particles set down, stick and pack in the anti-sand groove. When a great deal of hot water is circulating in the well bore, liquid viscosity lowers and scale particles set down speed increases also. The slow-dissolved solid scale-inhibitor SY-2 and anti-scale pump with long plunger-short barrel are developed and applied in field. Through these methods applications, the pump running time have been prolonged and good results have been achieved. Introduction ASP flooding technology improves recovery rate dramatically 1. However, alkali in ASP solution reacts with both formation fluids and mineralogical components such as kaolinite, montmorillonite and feldspar, from which silicon and aluminum components are soluted into fluids 2. With the fluids flowing and surrounding condition changing gradually, scale forming in artificial lift wells, which causes pump sticking in sucker rod pumps and the work over periods decrease. For example, without any anti-scale methods after scaling, the average work over periods are 37 days in sucker rod pump wells in a test area of Daqing oilfield, which influence the production and cause low commercial effectiveness. Silicon scale forming characteristics of ASP flooding Analysis of scale samples The typical scale samples from the field are analyzed. The well-consolidated scales are flake-shaped macroscopically and scale layers are fline vertically. The scales from oil well are not a single composition. They consist of silicon scale, carbonate scale and organic impurities. Silicon exists as silicate or SiO2, Ca2+, Mg2+ exist as carbonate. Fe exists as its oxide or sulfide or carbonate. Na and K are adsorbed on the surface of scale as soluble salts. Water is not the ingredient of the scale but it exists as absorbed water or crystal water. The characteristic functional group of HPAM such as CO-, -CH2-, -CONH2 exists in the scale, but the content of HPAM can't be quantificationally tested by Amylum-Cadmium Iodide method. Influencing factors of silicon scale formation Considering the field conditions, Na2SiO3 solution and mineralized water are made up to different simulating produced water. It is described as bellow. The temperature, correlative ion concentration, pH is changed, and the influences of these factors to scale formation are given as following. The first is silicon-only solution. The second is Si, Ca2+ and Mg2+ solution.

Barium Sulfate Scale Removal at Low-Temperature

“…Barium and calcium minerals are commonly found with higher concentrations in the formation water than the seawater; moreover, a higher concentration of sulfate ions is commonly existing with the seawater than the formation water [7]. Many different types of scales are prevalent with the oil and gas field from the sulfate type as barium sulfate which is commonly called barite (BaSO 4 ), calcium sulfate (CaSO 4 ), and strontium sulfate (SrSO 4 ) [8,9].…”

Development of a Unique Organic Acid Solution for Removing Composite Field Scales

“…Iron sulfide is considered the common sulfide scale in the oil field. Sulfate scales are common scale types in the petroleum industry as barium sulfate/barite (BaSO 4 ), calcium sulfate (CaSO 4 ), strontium sulfate/celestite (SrSO 4 ), and gypsum (CaSO 4 ·2H 2 O), in addition to other scale types such as carbonates (CaCO 3 , MgCO 3 , and FeCO 3 ), oxides, and hydroxides of Fe and Mg. 8 , 9 Scale precipitation is controlled by the pressure and temperature condition, pH, chemical equilibria of the reaction, ionic strength, and the interaction exposure time. 10 Due to these controlling conditions for the scale precipitation, the location of scale is different based on the existing source and operation condition as the sulfate scales precipitated with the seawater injection system because of incompatibility of water sources and this is considered as a hard scale type due to its low solubility with acid.…”

Variations of Micropores in Oil Reservoir Before and After Strong Alkaline Alkaline-surfactant-polymer Flooding

“…ASP flooding as applied to the EOR method is accompanied by a series of challenges. Longtime used ASP flooding increased pump-sticking frequency, which made oil production cessation [19]. Furthermore, scaling formation and permeability damage [20,21] derived from ASP flooding create an added area of concentrated concern and are not entirely understood [22], so to analyze the important control factors of permeability damage, micropore structure, during ASP flooding is necessary for well application of ASP flooding for EOR.…”