Application of Innovative Leaching and Resource Utilization Technology to Treat Oily Drilling Cuttings on the Harmlessization Handle in the Tian Mountain Front Block in West China
Authors: Long Li , Da Yin , Lei Li , Yuping Yang , Xianguang Xu , Jie Zhang 
Published: October 2017

The environmental impact of the use of oil-based mud (OBM) is one of the main challenges facing petroleum industry. One of the most difficult environmental problems to resolve at the well site is the disposal of oily cuttings, which are often physically unstable and unsuitable for landfill. Waste cuttings can not be left at site untreated. They carry with them potential environmental liability when improperly managed or disposed.

Drilling cuttings contaminated by OBM are treated to remove oil phase prior to discharge into the environment. Recently, China legislation has set the limits of total petroleum hydrocarbon (TPH) of permitted oil associated with discharged well cuttings to 2%, with a view to substantially reducing this limit further in the near future.

Given the geological conditions encountered in the super-deep formations in the Tian Mountain Front Block in Tarim Basin, the use of OBM is virtually essential if drilling is to be cost effective. A reduction in discharge limits to significantly below 2% can not be met economically by existing cuttings treating technology, so cuttings will be returned to land for disposal.

A new kind of solvent is developed for treating oily cuttings, and it can dissolve diesel and surfactants in oily cuttings effectively. Moreover, it can be separated from diesel rapidly by distillation. Innovative leaching and resource utilization technology (LRUT) is currently applied to treat oily cuttings in this Block. Most of the expensive OBM could be recycled by use of the frequency multiple-effect centrifugal process system, and the cuttings with the oil content of less than 10% are obtained. Then solid-liquid separation is achieved by using proprietary solvent leaching process and equipment technology, so the treated cuttings with low levels of oil and liquid phase containing diesel and solvent can be obtained. Moreover, the solvent can be recycled from the oil phase by means of the interphase mass transfer separation.

The results indicate that the oil content of treated cuttings is less than 1%, and the recovery rate of OBM is over 20%. The recovered oil components can be used to prepare OBM, and the treated cuttings can be used to pave the road, or used as raw material for producing cement or plaster. LRUT technology is characterized by high mud recovery rate, no secondary pollution, easy separation between the solvent and diesel, and it is very suitable for harmless treatment of oily cuttings. LRUT technology can not only recycle and reuse OBM resources, but also guard against environmental pollution from drilling operation by use of diesel oil-based mud, and thus produce great economic and environmental benefits.

LRUT treatment plant for oily cuttings is built in this Block, and its handling capacity can be up to twenty thousand cubic metres per year. As a result, LRUT technology can provide a powerful technical support for achieving safety drilling in this Block, and it has been successfully applied to treat oily cuttings from dozens of wells in this Block. This paper presents field data to illustrate the application of this technology and evaluate the potential technical and economic benefits that it might provide to petroleum development and production in West China.