November 21, 2008
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Home / Issue Archive / 2006 / November #11 / Sensitivity Analysis of Operating Factors, Which Affect ESP Performance in Unstable Low-production Oil Wells

№ 11 (November 2006)

Sensitivity Analysis of Operating Factors, Which Affect ESP Performance in Unstable Low-production Oil Wells

Lately, the Borets company has significantly enlarged the range of products for oil production from wells with various complicating factors.

By Misho Solesha, V.V. Gerasimov

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Therefore, the specialists of the company arrived at the necessity to develop an analysis technique for major parameters affecting the performance of submersible pumping units. The given technique is based on sensitivity analysis (study of effect of the selected parameters on the system performance) aimed at evaluation of the effect of interrelated parameters of the reservoir, well and pump on production results and system performance.

For example, when the developed technique for the sensitivity analysis was tested on problematic wells in Nizhnevartovsk region, submersible pumps with highly efficient pressure-dispersing (HEPD) stages were used in those wells.

Firstly, the well operation is analyzed. Then, a submersible pump with HEPD stages is run in the well, and its operational data is collected. On the basis of the acquired data, the expected pump overhaul period is predicted, and an overhaul period matrix is built, which will enable selection of the wells for sensitivity analysis of operating factors.

As the result of sensitivity analysis, we can compare operational data of the well and modeling results. In case of obtaining the well model, it becomes possible to determine the limits of operating parameters and consequently to balance well instability. This analysis results in recommendations and actions required to improve well productivity.

Approximately 30 wells were analyzed as a case in point. As shown in Fig. 1, there are wells with a very low overhaul period. In this case, the analysis is aimed at identification of parameters decreasing the system non-failure operation time.

As a rule, the well overhaul period is reduced by high content of solids and high water cut (Fig. 2), but sometimes it is necessary to get additional information on the physical properties of solids (hardness, shape, type), to be able to identify the cause of a failure.

Variation of fluid levels is the main parameter for sensitivity analysis. There is high variance in fluid level measurements; thus, a range of fluid level variation (+20 percent) was defined with a view to apply the developed technique.

Well production rate with a (+15 percent) range was selected as another parameter for sensitivity analysis. These two parameters significantly affect the pump performance and determine selection of the necessary equipment. Fig. 3 gives the data of well 8895 and the time-between-failures of various pumps run in this well during a three-year period of production. Unit parameters are calculated on the basis of this data.

This figure shows a solution region for the given system depending on the range of variation of sensitivity analysis parameters. In other words, variation of the dynamic level and production rate determines the level of variation of the unit parameters. This is important for low-output pumps, as small variation of parameters can account for wrong selection of the equipment.

Detailed analysis of the measured production rate and dynamic level proves that working points move along the performance curve.

Operational history and modeling results (obtained with the help of the software for the system analysis and selection of equipment) showed that unstable well operation, production decline, and failures of submersible equipment components are essentially related to a variation in the characteristics of fluid inflow and a high content of solids. It is recommended to use a variable speed controller and downhole sensors to control the well operation and regulate the pump performance in accordance with changes taking place downhole. It is best to apply an integrated approach to selection of appropriate equipment, monitoring of remedial operations, and installation of the equipment as integrated services of Borets group.

The results of the analysis are used to determine proper strategy for operation of pumps with HEPD stages in low-production wells.

 

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