Drilling and production operations in sensitive areas require an effective and efficient waste management plan to minimize the impact on the environment, especially when environmental legislations are strict. Waste management is a decisive factor during oilfield planning operations from an environmental and economic perspective. Often, the waste management method used depends on the type of operation (exploratory drilling, development drilling or production) and the environmental regulations. The waste related to drilling operations can include solid waste such as drilling cuttings and chemical products used for drilling fluid preparation, and liquid waste such as drilling fluid, contaminated rainwater and rig washes. Production waste comprises (mainly) completion fluids, produced water and oil-contaminated fluids. Cutting re-injection (CRI) technology is an accepted method for disposal of drilling cuttings and drilling-associated liquids. Produced water is usually injected into a subsurface formation for final disposal or to maintain reservoir pressure during production.
According to conventional oilfield practices, both disposal options occur separately in different wells. Currently, commingled injection of both drilling cuttings and produced water in a same well is an interesting option if it is properly addressed.
The article presents the commingled re-injection of cuttings and produced water during the development stage of the Pirana field as a cost-effective and environmentally friendly waste management method. The development of the Pirana field began in 2013 with seven producer wells and one injector well. During the 2013 campaign, the injector well was dedicated to only the re-injection of cuttings. After production started (at the end of 2013), the well was dedicated to only produced water injection until the beginning of the second drilling campaign (in 2014), where five additional wells were drilled and commingled injection began in the same injector well. Produced water was injected with periodic injections of drilling waste.