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How to Dispose Waste in the Domestic Drilling Industry?

Sep 24, 2013

At present, environmental protection is a basic state policy in China, and it has been a strategic mission and goal for our country to maintain a sustainable development of society, economy and environment. Along with the continuous improvement of environmental laws and the increasing environmental awareness among people, the departments concerned have successively enacted various environmental protection regulations to impose stringent limitations on waste discharge during well drilling and well completion.

During the process of oil exploration and production, a large amount of waste is usually left at well sites, which is kept in sewage pits. However, the poorly treated solid waste may have a bad effect on underground water and surface water, endanger the surrounding ecological environment and even cause pollution accidents when sewage pits leak, overflow or are inundated due to rain wash during the rainy season. Therefore, it is now a very important task for oilfield enterprises to take relevant waste management techniques to fight against the harmful waste and reduce its harm to environment to the greatest extent possible.

In recent years, although domestic onshore oil and gas regions have devoted great efforts to management of waste generated in well drilling and well completion, the techniques still remain too inefficient to dispose waste thoroughly. Nowadays, domestic and foreign waste management solutions differ greatly in technological solutions, supporting equipment and environmental investments. 

Most domestic oilfields have been directly solidifying the waste in sewage pits after well drilling and well completion. When the waste in sewage pits falls into clear liquid and sludge by natural sedimentation under the effect of gravity, drain the upper clear liquid less than 1/3 of the total, and then directly add curing agent into the remaining sludge for solidification. Since the waste to be disposed contains much water and consumes lots of chemical agents, the solution costs much, achieves unsatisfactory results and fails to completely eliminate pollution risks.

Facing local governmental requirements on environmental protection, domestic onshore oilfields now attach more and more importance to harmless drilling waste management and as a result, the disposal technology with solid-liquid separation as its core is applied to the drilling waste management, which replaces the out-dated direct solidification with the process integrating chemical method, solid-liquid separation and solidification method.

Solid-liquid separation is a key link in drilling fluid treatment. The more water you eliminate from waste, the less solids you get and the less money you pay. In this way, the disposal cost will be effectively controlled and more economic benefits will be obtained. Over the years, such dewatering equipment as orifice filter press, filter belt dewatering conveyor and decanter centrifuge have been developed successively in China, facilitating the disposal of drilling waste.

This solution proceeds as follows: natural sedimentation happens to sewage pits, free water produced by natural sedimentation undergoes routine sewage treatment, the sludge is chemically destabilized by flocculant and coagulant aid, centrifuge, filter belt dewatering conveyor or orifice filter press further separates solids and liquid, and finally the separated solids and liquid will be solidified and treated respectively. For this solution, the dewatering equipment is still on trial and yields lower efficiency for its low degree of automation.

Therefore, high efficiency relies on both reducing waste at the source and disposing waste during drilling. By combining overseas advanced experience with domestic practical drilling conditions, Xi’an KOSUN Machinery Co., Ltd., as a manufacturer of oil drilling-production equipment and solids control equipment, has customized an integrated drilling waste management solution for customers.

The solution begins with the source and consists of the following four steps: solid control equipment - dewatering/water treatment/water recycling/filtration – mud recovery - stabilization/biodegradation/thermal desorption/cuttings reinjection.

In the process of drilling, KOSUN Solids Control System directly connects to the outlet of mud pump, performs four-stage solids control treatment on the mud, effectively recovers mud as much as possible and minimizes the waste.

The mud treated by solids control equipment can be directly put into use, and the dewatered waste can be directly delivered by conveyor to Hi-G shale shaker and vertical cuttings dryer for further solid-liquid separation. The separated water can be recycled after being treated by purifying equipment. The waste residues become very dry after being treated by Hi-G shale shaker and vertical cuttings dryer, and can be finally disposed by means of solidification, biodegradation, thermal desorption and cuttings reinjection, by which the zero discharge of waste is achieved.

Compared with the first two solutions, this one starts to treat waste at the source, reduces the waste discharge, enhances the efficiency and saves much drilling cost. Meantime, the full use of dewatering solution on further waste treatment effectively recovers water resource, reduces water content in waste, shrinks waste volume and protects the environment well. The goal of zero waste discharge is realized through solidification, biodegradation, thermal desorption and cuttings reinjection of the remaining waste solids. Moreover, the application of solidification in onshore drilling and cuttings reinjection in offshore drilling meets the actual requirements at drilling sites, with stronger practicability and higher efficiency.