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Abstract

Many small independent operators are currently using a cookbook style of production operation and performance evaluation. The result reduces the opportunity of producing at the well's top performance which will curtail the current revenues. A promising innovative Nodal analysis technique is being applied to two Appalachian gas wells uni microcomputer. The objective of this paper is to present the optimization studies and their effect on production operations.

Wade #2 well was drilled and completed in 1985 in Harrison County, West Virginia. The well was hydraulically fractured in 3 zones, Benson, Balltown, and Speechley and the stimulation seems to be working well. A 2-3/8 inch tubing string was run to a depth of 4774 feet. The well was loading with fluid and producing at a diminishing rate. It in suspected that oil is being produced in the upper zone which causes damage in the lower zones (gas zones). If the oil is isolated from the other zones, the gas will not have enough pressure to produce by itself. The Nodal analysis suggests that the well's production will be improved if an intermittent gas lift "rabbit" in installed for the production stream. The well will then be producing efficiently in different zones.

Pratt #1 well was drilled and completed in late 1985 in Lewis County, West Virginia. The well was stimulated in two zones Balltown and Speechley, with hydraulic fracturing. Since the engineer believed the well could be a better well from the logging data, a deep penetration stimulation was conducted on this well. Unfortunately, the well started producing water, and the oil and gas rates dropped because the fracture had gone into the water zone in the neighboring area. If a casing log is run in order to find out the exact location of the water zone, the well needs to be cement squeezed, reperforated and restimulated in the new zone. However, this method would be very costly. The Nodal analysis was applied for this well. Clean-up and stimulation will be necessary to remove the wax and formation damage. Again, an intermittent gas lift is recommended to replace the sucker-rod pump. With all theme recommended changes, the well will be producing at its optimized rate. In addition, both wells' new designs will have an economic advantage over the old design without excessive extra cost.

Introduction

Nodal analysis is a system analysis approach which can be used to optimize a production system, such as an oil or gas well. Every component in a well of a producing system in included and analyzed in order to achieve the most desirable rate with the highest economical return.

Figure 1 shows components that make up a producing system. The system begins with the reservoir and proceeds to the separator, the components are broken down as:

  1. reservoir pressure

  2. well productivity

  3. wellbore completion

  4. possible downhole restrictive device

  5. tubing

  6. safety valve

  7. tubing restriction

  8. surface choke

  9. flowline

  10. separator

To optimize the system effectively, each component must be evaluated separately for the entire production system. The effect of the change of any one component can be very important and will be able to display graphically. In the analytical system, a node is set for the inflow and outflow streams. All the components upstream of the node comprise the inflow section, while the outflow section consists of all components downstream of the node.

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