THEORETICAL DRAWDOWN OF A HORIZONTAL WATER WELL WITHIN A DEEP CONFINED CLASTIC AQUIFER

Horizontal well drilling was developed in the petroleum industry to obtain oil from thin reservoir units that otherwise produce low yield. Horizontal drilling can possibly provide an increase in well productivity and a higher yield of petroleum recovery than can be obtained from a vertical well. Horizontal drilling has been recently applied to the exploitation of groundwater and its use represents the cutting edge of techniques for the water well industry. Understanding and predicting the impact of pumping horizontal wells in a confined aquifer can be complex because horizontal well geometries are similar to partially penetrating vertical wells and horizontal well functions have not been adequately developed. This study focuses on the geometry of the drawdown of a horizontal water well due to high volume pumpage from a deep confined clastic aquifer.

Several mathematical formulae for the determination of drawdown for a partially penetrating well in a confined aquifer were analyzed to see if they could be applied to a horizontal well. Hantush’s method of drawdown for a collecting well was also considered. A small-scale physical model representing a deep sand aquifer confined by clay was constructed to support the mathematical analysis. The model includes small fully penetrating monitoring wells placed around the pumping well to monitor the potentiometric surface changes. Another small-scale model with partially penetrating monitoring wells was used to compare the results from the first model. The simulated aquifer was pressurized to observe the changes in the potentiometric surface while the horizontal well was pumped at a constant rate. Data were then applied using the Theis method to show the change in drawdown with respect to time and compared to the Theis curve for a vertical partially penetrating well.