Impact of waste drilling mud on the environment

A large amount of drilling waste is inevitably generated during the oil and gas extraction process, of which nearly 50% is directly discharged into the surrounding environment. If not properly handled, it will have a serious impact on the surrounding soil environment, water environment and plants, especially the soil environment.

Because the waste mud contains excessive soluble salts and alkalis, this will cause the soil in the discharge area to become salinized, resulting in an increase in the total mineralization of the soil system, causing soil compaction, and ultimately leading to a significant reduction in crop yields, the inability of wild plants to grow and reproduce normally, and serious degradation of soil quality. Moreover, excessive soluble salts and alkalis will break through the limited adsorption and interception capacity of the soil after being washed and leached by rainwater, and migrate to deeper levels of the soil, thereby polluting groundwater.

Certain additives and cuttings in drilling fluids also carry a certain amount of heavy metals. These heavy metal ions may undergo a series of complex physical, chemical, and biological reactions with the soil. When accumulated to a certain extent, they will affect the growth and metabolism of soil microorganisms, inhibit their activity, and further change the biomass of microorganisms, thereby changing the community structure and function of local soil microorganisms. What is more serious is that the synergistic effects between heavy metals in the soil are often more toxic. For example, Zn-Cr composite pollution will inhibit soil enzyme activity and significantly reduce soil fertility.

In addition, the heavy metal pollution process in the soil is not only very hidden, but also lasts for a long time, which may lead to its enrichment in the human body through the food chain. If the waste drilling mud is discharged into the water environment without treatment, it will also bring a series of environmental problems. The content of suspended matter such as clay and bentonite particles carried is very high. These suspended matter are in colloidal form and are usually stable in the water. They can exist in the water for a long time, making the water turbid and greatly reducing the self-purification capacity of the water.

Additives, organic matter and their decomposition products in waste mud cause its COD content to exceed the standard by dozens or even thousands of times. These organic matters discharged into water bodies will cause eutrophication, promote the proliferation of algae, greatly reduce the dissolved oxygen content in water bodies, and lead to the deterioration of internal circulation of water quality, resulting in the death of a large number of fish and other aquatic organisms, causing the water body to stink and turn black; some waste drilling mud contains petroleum substances that exceed the standard by hundreds or thousands of times. Discharging into water bodies will isolate the exchange cycle of oxygen in the air and dissolved oxygen in water, and its oxidative decomposition will consume a large amount of dissolved oxygen, resulting in a decrease in dissolved oxygen content, thereby causing harm to the survival of aquatic plants and animals; heavy metals in waste mud will also pollute surface water through leaching and runoff, causing the water quality environment to deteriorate, and will be enriched in aquatic plants and animals, and then affect human health and safety through the food chain.

The impact of waste drilling mud is also reflected in the fact that the heavy metals it contains have an inhibitory effect on plant growth and development. For plants that need seeds to reproduce, heavy metal Cr inhibits seed germination by inhibiting the activity of amylase and the movement of sugars in the hypocotyl. Heavy metals that enter the plant body may inhibit the photosynthesis of plant leaves, reduce the activity of multiple enzymes in the plant body, and change the permeability of cell membranes, thereby affecting the normal growth and reproduction of the plant.

Although waste mud contains calcium, magnesium ions, phosphates and other ingredients that are conducive to plant growth, and its organic matter can be converted into humus after being decomposed by microorganisms and can be used as a source of nutrients for the soil, the ability of plants to absorb nutrients from it is very low, so these nutrients basically cannot be directly absorbed and utilized by plants.