The gas industry in the Appalachian Basin is experiencing falling gas prices. The result is reduced revenues and fewer dollars available for exploration and development of new reserves. This has forced innovative companies to examine methods to increase production from existing wells. It has been observed that optimizing a fluid removal program can result in profitable production increases.
The majority of accumulated fluids in the wellbore are formation salt brines. The hydrostatic pressure created by this fluid column can restrict or kill production from these typically low pressured reservoirs. The most common procedure used to remove the production reducing brines is periodic bailing.
The non-linear least square curve-fitting techniques are being applied to fit the production decline of each well. The overall production is curve-fitted as hyperbolic or harmonic decline and each bailing cycle is curve-fitted as an exponential decline. The bailing cost and other economic overhead are used as the economic limit for bailing cycle scheduling. Other criteria such as rate of return on investment, lease contracts, current gas prices, geographic location, weather conditions and farming activities will be optimized into a working priority lint for the bailing operation of each well. The ultimate goal is to create a complete management package on a microcomputer that can be used to continuously evaluate the update the entire bailing and production maintenance program. In this package, artificial intelligence will be included to optimize the decision-making rules. This now approach will create an economic benefit for oil and gas production in the Appalachian Basin. This paper describes the development and work completed towards this objective.
Many of the producing gas wells in the Appalachian Basin have been in production over 25 years. Most of these wells produce dry gas with little or no condensate. The formation water ranges from slightly brackish to 50% saturation. The producing formations are low permeability, low porosity and are showing signs of field depletion. The wells tend to produce at a marginally economic volume level and at pressure slightly above line pressure.
Reservoir pressure depletion has also allowed formation water invasion to take place. The low pressure and low velocity production conditions also allow formation water to accumulate in wells. This accumulation, if left unchecked, will eventually create enough hydrostatic pressure to choke off gas flow at the sand face and force fluid saturation in the pay zone adjacent to the wellbore.
It has long been standard practice in the Appalachian Basin gas fields to bail or swab this brine water from the well. (Although "bail" and "swab" are different methods, the word "bail" will be used to include either operation for simplicity.) The objective in to remove the hydrostatic restriction from the well and reduce capillary pressure restriction in the immediate wellbore area. This operation in the single most effective production improvement method that can be used on this type of gas well.
Currently, the Consolidated Gas Transmission Company has approximately 2000 wells in its bailing program in the West Virginia and Pennsylvania operating area. Each well may need bailed from 2 to 8 times per year. This is equivalent to 4000 or 5000 bailings being performed annually by 25 – 30 bailing machines located in various field operation districts.