Thomas Kwader says developing horizontal wells is difficult for a number of reasons, mainly because the bentonite drilling mud used during the drilling of the borehole is extremely efficient at plugging holes or slots on the screen..

Traditional vertical water producing wells are often difficult to fully develop. Horizontal producing wells are much more difficult to even partially develop. Developing horizontal wells is difficult for a number of reasons, mainly because the bentonite drilling mud used during the drilling of the borehole is extremely efficient at plugging holes or slots on the screen. When the borehole is initially drilled and drill mud is circulated through the borehole, a thick (up to1-inch) gel cake is "built up" on the formation wall. This mud cake is similar to Jell-O in appearance and is very low in permeability. Pulling the horizontal well casing and screen through the borehole "smears" the openings on the well screen shut. In order to effectively develop the well, the openings must be cleared of the gel and the majority of the formation gel cake must be removed from the borehole by a flushing of the borehole annulus and/or pulling the gel through the screen openings - a near impossible task.

The introduction of a polyphosphate (see a drilling mud supplier for different brands available) will help breakdown the gel strength of the mud, but the bentonite and natural clays still need to be removed from the borehole annulus. Another method used to place the polyphosphates outside the screen is to pull a tremie pipe (3/4- or 1-inch) attached to the outside of the well casing. Small diameter holes drilled in the tremie pipe along the screened area allow for the polyphosphates to be injected where they are needed. Leaving the polyphosphates overnight helps break down the gel.

Jetting (high-pressure water) the inside of the casing is useful in blowing out the screen if the tool is properly designed; however, the mud still needs to be removed from the annulus or the plate-like clay particles will eventually reseal the screen.

Pumping clean water and polyphosphates into the well casing using a centrifugal pump under pressure (40 psi to 60 psi) to blow open the slots has been effective, especially if the casing can be pressurized and held for a few minutes. We also have found that using a submersible pump (and well seal to maintain pressure) to evacuate the casing quickly promotes a surging action that helps clear the openings from mud in the borehole annulus.

Fortunately, the screened surface area on horizontal wells is usually quite large, and the need for a horizontal well to be fully developed is not as critical as a vertical well to operate efficiently.