ENGINEERING AND HYDROGEOLOGIC CONSIDERATIONS AS RELATED TO WATER WELL PRODUCTION AND WELL REHABILITATION

The geologic history of the surficial rocks and sediments which cropout throughout Texas is the result of a complex history of repetitive sequences of geologic phenomenon which include uplift or mountain building, followed by erosion and transgression and regression of the seas.  As a result, 7 geologic formations have been identified throughout Texas as mayor aquifers and 17 as minor aquifers.

 

Texas Major Aquifers

 

The chemical and hydraulic conditions within these aquifers have for many years been in equilibrium (a balanced system).  The aquifers supply 59% of the water needs for the state of Texas in 2004 and as a result of this production, an imbalance in the naturally occurring systems have occurred which has altered hydraulic and chemical properties of the aquifers.  This has resulted in localized areas with problems and more regional problems such as the critical groundwater areas designated by the Texas Department of Water Resources.

 

Percent Groundwater Use

 

These aquifer problems include those related to water quality and declining groundwater levels.  Both types of problems can result in well production decline and have similar symptoms as those related to well aging.  Therefore, the questions are:

 

• Are they aquifer or well aging problems,

• Can they be solved and

• Are they considered in the well rehabilitation program

By developing a strategy for rehabilitation prior to commitment of funds for rehabilitation, intelligent decisions can be made between rehabilitation methods versus other alternatives based on cost effectiveness and economics.

 

A simple six step program is suggested to develop a well rehabilitation strategy. The program is based on sound engineering principals and utilizes a computer modeling to simulate well performance. The model can be utilized to identify, evaluate and solve well decline problems related to aquifer and or well aging.  Based upon this modeling, a strategy for well rehabilitation is developed which provides owners of wells with information to evaluate the economics of a rehabilitation program compared to the potential increase in production or a no action alternative or a new well.

 

Additionally, the procedure provides a system of checks and balances to the expenditures of funds during the rehabilitation program by carefully monitoring and evaluation of that program.  This same methodology can be utilized to anticipate well decline problems for new wells. In that since, well design and construction can take into account anticipated problems in the future.

 

WELL REHABILITATION STRATEGY

STEP 1 - SIMULATE EXPECTED WELL PERFORMANCE WHEN BUILT

·        COMPARE TO ACTUAL PERFORMANCE WHEN BUILT

·        DEFINE DESIGN/CONSTRUCTION LIMITATIONS

STEP 2 - SIMULATE WELL PERFORMANCE AT PRESENT   

·        DEFINE REGIONAL AND WELL RELATED LIMITATIONS

STEP 3 - SIMULATE WELL PERFORMANCE AFTER REHABILITATION