A Beginner's Guide To The Borehole Drilling Process in Zimbabwe

We have taken the time to compile the information that you will need to put your mind at rest before you make an informed decision. 

There are several steps involved between the moment you decide to invest in a domestic borehole, and getting water pumped out of the earth. We thought it beneficial for our clients to understand the steps involved, so we outlined the steps below:

1. Site Survey: Before borehole drilling, there is a need to conduct a Hydro-Geological Survey at the proposed site. Generally, groundwater is unequally distributed surveys ascertain suitable sites for the exploration of significant quantities of groundwater before carrying out any drilling exercise.

This ensures the best spot is selected according to the geological data and our clients’ plans. The hydro-geological data, maps, graphs and cross-section profiles obtained from the hydro-geological survey are used in the determination of important information such as estimation of drilling depth and Identification of stress areas

2. Site Mobilization: Site Mobilization consists of preparatory work and operations necessary for the movement of personnel, equipment, supplies, and incidentals to the project site.

Mobilization includes the transferring to the job-sites of all equipment, plants, supplies and materials, personnel, and all items necessary for the execution and completion of the work, and shall also include the setting up of all equipment, instruments and all other plants until rendered operable, subject to the confirmation of the Engineer.

3. Ground Breaking and Drilling: It is only when the rig is complete set up that the workers can begin the operations for the drilling itself. It all begins in the starter hole where a surface hole is drilled down to a specific measurement. Afterwards, the stages of drilling are continued.

Rotary using the mud flush technique (Mud Drilling)

A Beginner's Guide To The Borehole Drilling Process in Zimbabwe

Here, a drill bit made from tough materials is attached to the end of a drill pipe. When the process is started, the driller waits until the bit is moving across the substrata. Once it has been confirmed, some drill fluids are passed through the drill pipe, into the hole and then back to the surface. This process is very important as it washes the residue and cuttings back to the surfaces. The fluid has many purposes including the fact that it gives lubrication for the drill bit.

Rotary with air percussion and flush (Air Drilling)

This method makes use of compressed air to help break up hard rock formations. This borehole drilling mode requires the skills of an expert. Compressed air is usually used to operate an air hammer which is situated deep down the hole. The same air is what will eventually blow the crushed fragments as well as water up the hole that is being created.

4. Rock Sampling: The collection of representative subsurface samples is key to the development of relevant and accurate geotechnical evaluations and assessments. As the drilling process continuous, geological rock samples are taken at set intervals. Struck and water rest levels are constantly recorded. This process enables us to estimate the yield of individual aquifers encountered.

Borehole Casing: The Borehole Casing process keeps the Borehole open and protects the earth, similar to the efforts to protect groundwater. The hard metal casing shores up the borehole and extends through both the verticality and the horizontal drilling phases, assuring the long-term integrity of the Borehole from end to end. In addition to providing stabilization and keeping the sides of the Borehole from caving in on themselves, the casing protects the borehole stream.

5. Borehole Development: Developing a Borehole is the process of removing fine soil particles, drill cuttings, and residual drilling mud from the Borehole screen and borehole annulus in order to establish a good hydraulic connection with the surrounding formation. This development aims at repairing the damage done to the aquifer during the course of drilling by removing additives from the borehole.

6. Capping and Slab: The final stage of borehole drilling requires the pumping and piping of water from the successful borehole. The end use of the water will largely determine the type of pumping and reticulation system that will be installed. With too many variations on the nature and type of pump installations to go into detail here, we will discuss the most appropriate options with you in person. Contact Export Hydro to learn more about this process towards investing in your own borehole.

A Beginner's Guide To The Borehole Drilling Process in Zimbabwe

7. Test Pumping: Test Pumping involves pumping a Borehole from a measured static water level at a known yield and recording the rate and pattern by which the water level within the Borehole changes. Once a dynamic water level is reached, the rate of inflow to the Borehole equals the rate of pumping. Towards the end of the test, a water sample is collected for chemical analysis.

The duration of the test is 24 hours, with a further 8 hours for a recovery test. 

The results of the test enable the hydrogeologist to calculate the best pumping rate, the installation depth, and the drawdown for a given discharge rate.