| Sulige Gas field is a large-scale gas reservoir with low porosity, permeability, small yield, low abundance and lithologic traps. With the development, formation pressure gradually decreased, water yield generally produced, and the effusion in wellbore seriously appeared, which lead to a sharp decline in gas production. Relatively, foam drainage gas production technology which is one of the top ten key technologies in Sulige, has lower cost.The principle of the foam drainage technology is that the foam agent solution was injected into the bottom wells, gradually contacting with the fluid in wellbore. At the stirring action of the natural gas stream, a large amount of foam is produced, which is relatively stable and low-density in the role of surface active agent. The gas-liquid distribution within the tubing is changed. As a result, the fluid pressure is dispersed, which lead to back pressure reduces. The friction loss and borehole gravity gradient also reduces in the bottom of the well, which causes a good result and less energy consumption. The difference of production pressure of gas well increases, which directly brings another good result that the output of natural gas increases. And the gas perforce better in liquid-carrying. Finally, the effusion in the bottom hole partially or completely is moved out, and the regular production of gas well restored. Additionally, the foaming drainage agent can also make the insoluble soil, such as sediment and sludge, wrapped in the foam and discharged along with the airflow, which contributed to achieve stable production and dredge the passage of gas flow and water flow.Foam drainage gas recovery technology is a chemical method to solve the problem of liquid-carrying in the middle/late development stage. With the technology continues to be mature and widely used, the types of foaming agents constantly updated, the dosage constantly reduced, but the result became better. However many factors had negative effects on the foam drainage agent application in the real world, such as high temperature, salinity, condensate oil content, methanol content. The conventional foaming agent was unable to meet the requirements of site conditions, which was more and more serious. This paper aims to develop a suitable foaming agent which won’t be effected by extreme environment, such as high temperature (>90℃), high salinity (>20×104mg/L), high calcium ion concentration (>1.0×104mg/L), high condensate oil content (50%). And its drainage technology is also researched, trying to find an affordable and efficient way to exclude the downhole fluid and maintain the wells longer-term stable production. First,26single surfactants were screened in this paper to look for an effective blowing agent, which included5non-betaine surfactants and21betaine surfactants.The salinity of simulated formation water was16×104mg/l, calcium ion content was1.0×104mg/l. Betaine surfactants had better foaming performance. The result of initial screening is T-YGAP-2, T-HPPE14, T-YYAP-1, T-YYAP-4, T-APHPS18. The foaming and stability of the five active agents were compared at0.1%,0.2%,0.25%,0.30%. As the concentration increased, the initial height Ho increased which meant that foaming capacity enhanced. When the concentration was0.25%, the initial foam heights were more than130mm. When the concentration was higher than0.25%, the foaming capacity enhanced slower. The difference of foam height at3min,5min,8min decreased, which means the foam stability gradually increased. Increasing the concentration of active agent might be beneficial to enhance its stability.T-HPPE14performed well under four concentrations. The foaming and stabilization of T-YGAP-2, T-YYAP-1, T-YYAP-4and T-APHPS18enhanced with concentration, which meant that they made better performance at higher concentration. Under the same experimental conditions, T-YGAP-2performed best in foaming capacity, T-APHPS18worst, and T-HPPE14perform best in stability, T-YGAP-2worst. Therefore, the screening experiment of single blowing agent had a result of T-HPPE14, T-YGAP-2, T-YYAP-1and T-YYAP-4. With the same standard method, the result of screening experiment of single foam stabilizer was YGAPOA and OA, from12stabilizer agents.Then, four foaming agents and two stabilizers were mixed by1:9,2:8, to9:1. At room temperature, the salinity of simulated formation water was16×104mg/l, calcium ion content was1.0×104mg/l, T-HPPE14and OA, T-HPPE14and YGAPOA, T-YYAP-1and OA were the only three, which were suitable for complexing because of their better performance than single foaming agent. The optimal ratios of complexing respectively were7:3,7:3and9:1. Others performed worse than single agent when they were complexed at any ratio.At90℃, the ratio was different. The optimal ratios were5:5. When T-HPPE14and OA were complexed with the same proportion, the maximum foam height was291mm, the foam height of3min,5min,8min were respectively251mm,234mm,220mm. The foaming and stability were the best at this time. T-HPPE14and YGAPOA with the same proportion, the maximum foam height was290mm, the foam height of3min,5min,8min were respectively251mm,230mm,98mm.The foaming performance was good and foam stability was good Within five minutes, too. But the foaming stability slipped down quickly within eight minutes. When the ratio of T-HPPE14became greater, the overall stability of foam formula enhanced. T-YYAP-1and OA with the same proportion, the maximum foam height was271mm, and the foam height of3min,5min,8min were respectively120mm,104mm,39mm. Compared with the foaming capacity, T-HPPE14and OA, T-HPPE14and YGAPOA had better performance.Under the same conditions, T-HPPE14and OA with the same proportion, the anticoagulation oil capacity did not exceed30%while T-HPPE14and YGAPOA could reach50%. So the main agents were made, T-HPPE14and YGAPOA complexing with the same proportion. In order to enhance the capacity of the foam formula, other additives were studied and added with small amount. From Carboxy Methyl Cellulose, Polyvinyl Alcohol, Povidone, Triethanolamine, N-dodecyl alcohol, the first two were poor compatibility with the main agents. The foaming and stability of the last three were compared at0.01%and0.001%. Povidone performed best at low concentration. So the final composition of foaming formula was T-HPPE14:YGAPOA:PVP=1:1:0.008.Seen by the evaluation experiments of foam performance, the application concentration was recommended ranging from0.20%to0.30%. And those properties were evaluated well which included temperature resistance, salt tolerance, anti-calcium capability, dynamic liquid-carrying capacity and oil anticoagulation. When the concentration was up to0.25%, the temperature resistance was more than90℃, salinity tolerance was up to20×104mg/l, anti-calcium capacity was up to1×104mg/l, anti-oil capacity was to50%, and dynamic liquid-carrying capacity was to550mL/15min with40%oil content mineralized water. These performance index values were greater than other foaming agents with good market reaction, far better than the industry standard values of qualified products.Five development wells in Su-25area were tested for foam drainage gas field trials. The technology was made up to inject foam formula from casing annulus with cars. Four wells, Su25-39-9, Su25-41-16, Su25-42-3, Su25-42-7, were succeeded, in which the downhole fluid was excluded fast and gas yield increased significantly. Su25-41-12was failed, which meant that this method was more suitable for gas wells with a certain production capacity and a certain level of effusion. Not all draining stages were fit to applicate this method, and not all wells were suitable for its application. |
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