Project for Upstream Subsurface Metal Loss Assessment - Essay Example

Project for Upstream Subsurface Metal Loss Assessment Defining the problem The number of injector and producer wells that have developed leaks in the last seven decades reaches approximately 30%. This percentage is obviously surprising when considering the production of oil from the oil fields rely on the efficiency of the wells. The development of the leaks occurs through the multiple concentric casings, which were once seen, as the most appropriate solution for improving production from the oil fields. The failure of these multiple concentric casings have triggered the involved authorities to integrate the use of various strategies such as; Attempting to improve cement placement practices; Random installation of corrosion resistant chrome C13 liners across the Umm Er Radhuma (UER) formation; and Indiscriminately utilizing impressed cathodic current protection (ICCP) systems. Even though many had strong belief in the effectiveness of these strategies, the realization is far more from the expectations. The impact of the strategies is a slight decrease in the number of leaking wells over the recent years. Further, the popular use of the rig-operated straddle packers is another available strategy used in locating downhole casing leaks. However, this strategy has proved less effective because it does not give an overall comprehension of the state of the leaks. The strategy might ignore the detection of additional intervals of serious corrosion, which may lead to leaks in the near future. Consequently, this means that there is need for a proper solution that will help in accessing the overall health of the downhole casing. 2. Developing a model In developing a model for solving the above problem, a variable and parameter were determined. Age was used as the parameter while Maximum Metal Loss % was the variable. EM technology, acting as a model, was used to logs from over 80 wells in one mature Middle Eastern offshore field, profiling the severity of measured metal loss (ML) from concentric casings against proven rig-discovered leaks and rigless measures of subsurface metal loss. The EM logging technology helps in forecasting and locating casing leaks that otherwise would have been detected only by conventional zonal pressure testing, with a high degree of probability. The significant of EM logging technology arises from the fact that it is more efficient and reliable. The evolution and advancement of a slim tool version in 2010 has unveiled a much more efficient and reliable diagnostic tool for exposing significant metal deterioration measured from within production tubing. Therefore, this technology offers an improved method for predicting the likelihood of potential casing leaks. The model helped in determining the maximum metal loss %, which is the variable. 3. Acquiring input data Of the over 80 wells logged with this EM technology, nearly 20 of them include proven double casing leaks confirmed by workover rig pressure testing.  A representative 8 of these wells were taken to articulate better analysis.  In every one of the leaking wells, massive corrosion anomalies correlated to a confirmed leak depth.  The mean range of measured maximum double casing ML for these leaking wells is 70% ML and the statistical mode is 62%. Of the wells logged with this EM technology, nearly 20 have ML greater than 50%, yet the casings are not yet leaking.  The range of measured maximum double casing ML for these non-leaking wells is 50-80%, where the mean is 60% and the mode is 57%. In acquiring the input data, the following frequency table was constructed from the data Total ML (All) age (row level) Count of Maximum Metal Loss, % (Y) 7-16 3 17-26 3 27-36 70 37-46 17 47-56 9 Grand Total 102 From the above frequency table a pivot chart was constructed In order to determine the volume of the total leak from each casing, Sampling and direct measurement were used. Direct measurement helped in measuring total ML of the subsurface leaks. In order to obtain data for the total metal loss, the EM tool was logged as a continuous pass at 1800 ft/hr from below 6270 ft within 7-in, 26 ppf casing. Then it was entered 3 and half in., 9.3 ppf tubin tail, then up past the tubing packer, and finally logging up into the 4 and 1/2., 12.6 ppf production tubing above 5,906 ft. 4. Developing a solution In developing a solution a regression model was constructed from the data as shown below: SUMMARY OUTPUT                                   Regression Statistics                 Multiple R 0.366365               R Square 0.134223               Adjusted R Square 0.12298               Standard Error 14.91318               Observations 79                                 ANOVA                   df SS MS F Significance F       Regression 1 2654.931 2654.931 11.93749 0.000898       Residual 77 17125.02 222.4028           Total 78 19779.95                                 Coefficients Standard Error t Stat P-value Lower 95% Upper 95% Lower 95.0% Upper 95.0% Intercept 78.77682 11.62698 6.775348 2.21E-09 55.62455 101.9291 55.62455 101.9291 Age(X) -1.16483 0.337135 -3.45507 0.000898 -1.83615 -0.4935 -1.83615 -0.4935                   The following is a residual graph which also helped in getting the R2, which is the coefficient of determination As the residual graph shows, the points concentrate around 0 meaning there is not significant deviation from the actual point hence the company should readily consider this project as viable. In developing a solution to the model, a EM RFEC technology was used to determine the massive corrosion associated with the casings. The EM technology is available for sensing metal dimension changes within three and sometimes four concentric pipes and it can read changes in metal thickness in casings as large as 13 inches outside diameter (OD). The tool body enables assessment of multiple body casing string without the costly removal of the production tubing. The logging tool also evaluates corrosion in any environment, including inside gas-filled tubulars. The following is a manipulation of the model in order to develop solutions. Double coil phase shift increases when logged across changes in increased metal thickness such as at collar joints, when entering from casing into tubing, when passing across a 3 and ½ - in. tubing packer, as well as when responding to slight thickness increase s at the 3 and ½ in. to 4 and ½ in. tubing crossover. Double coil amplitude decreases as signal attenuation is augmented because of the increases in available ferrous metal. When logging across double pipes such as this production tubing plus 7-in, casing, one can determine thickness anomaly is responding to casing collars versus tubing collars because separate casing collar, log measurement typically responds only thickness increase of the innermost pipe collars. 5. Testing the solution In order to test the validity of the solution, a regression test was carried out for the results obtained from interviews and those from the catalogue. Running a regression on the two data shows that there is a slight difference especially in the p value. While carrying out interviews the p-value for age 0.5, which is only 0.01 when using data from firm’s catalogue. This confirms the accuracy of the solution since a regression test shows there are insignificant differences between the original data and the additional data. The following is a calculation of coefficient of determination and correlation coefficient to help in testing the solution: Coefficient of determination is 0.19 x 100 = 19% Correlation coefficient Square root of 0.1909 = 0.4369 The coefficient of determination is 19%, which is enough indication that there is a significant relationship between metal loss and age. Significance F The significance F (0.000898) is far much less than 0.05. This indicates that the results from the project are reliable 24% of all evaluated wells have local intervals of severe corrosion similar to the wells with known casing leaks, yet these 24% do not have evidence of leaks. The range of measured maximum double casing ML for these non-leaking wells is 50-83%. Of the oil-producing wells studied in this research, nearly 20 completions were proven to have enough external casing corrosion to result in leaks.  The minimum measured, average circumferential metal loss of double casings was 52% for any well that leaked; therefore, any double casing with >50% corrosion should be considered compromised and close to hydraulic failure.  19 of the available wells evaluated fall into this near-failure category because double casing wall thinning is 50% or greater. 6. Implementing the results The following forecast was made for ages 60, 70 and 80 age maximum metal loss 60 31.81 70 34.30 80 36.89 The forecast shows that at age 60 the percentage maximum metal loss was 31.81% while that for 70 was 34.30%. The forecast depicts that there is a linear relationship between age and metal loss. The use of EM technology has proved significant in detecting corrosion in the case, thereby reducing the maximum metal loss from the wells. The company should seize the chance of using EM to monitor the number of leakings occurring from the casings. There should be close monitoring on these casings to avoid the costs associated with workover repairs. The results show that determination of hydraulic failure of any double casing depends on the EM-measured corrosion. 50% should act as the demarcation for determining whether a casing requires workover repair. In this case, any double casing with more than 50% corrosion results, as measured by EM technology, should be considered a candidate for a workover repair since this shows that it is compromised with and closed to hydraulic failure. Practically, this means that 25% of all wells logged so far include isolated intervals of greater than 50% ML and are therefore candidates for workover repair.  The degree of workover repair is highly dependent on the vertical length and severity of the corroded interval. If the managers of the company were to integrate this model in the operation of the oil field, then there would be reduction on cost, through the reduced number of workover repair and subsurface leaks. Read More