Fracture Optimization in the Valdemar Field Offshore Denmark

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 170981, “Fracture Optimization Reduces Completion Cost While Improving Well Productivity in the Valdemar Field Offshore Denmark,” by Dario Stemberger, SPE, Maersk Oil, and Pedro Saldungaray, SPE, and Terry Palisch, SPE, Carbo Ceramics, prepared for the 2014 SPE Annual Technical Conference and Exhibition, Amsterdam, 27–29 October. The paper has not been peer reviewed. The Valdemar field contains a target reservoir that is a Lower Cretaceous “dirty chalk” containing up to 25% insoluble fines, porosity greater than 20%, and permeability below 0.5 md. Stimulations on several wells showed suboptimal production rates, which led to the conclusion that the Lower Cretaceous was not economically producible. An intensive study was therefore carried out to evaluate all aspects of the fracture design and implementation. This paper focuses on the aspects of proppant selection and adequate fracture-conductivity placement, with the goal of improving well productivity and cumulative recovery. Completion Optimization The Valdemar field is located in the Danish sector of the North Sea. The reservoir is characterized by a heterogeneous sequence of argillaceous chalk with thin beds of marl and claystone. The Lower Cretaceous reservoir is subdivided into 14 reservoir units on the basis of nanopaleontology and sequence stratigraphy. Because of the Valdemar field’s suboptimal production rates, an intensive study was carried out in 2008. Numerous experts were invited to view data, perform simulations, and offer recommendations. Eleven key items were identified as areas of potential improvement and are detailed further in the complete paper: Improve the accuracy of treatment displacements. Implement aggressive fracturing-fluid-breaker designs. Improve fracture conductivity by use of resieved sand. Introduce real-time data acquisition and modeling. Enhance interpretation of minifracture analysis. Gather pressure data for afterclosure analysis. Minimize total fluids injected. Assess the use of ceramic screened sliding sleeves for proppant-flowback control. Supervise well cleanup. Institute quality-control procedure for completion brine. Introduce ceramic proppants for fracture-conductivity enhancement. A study by a third-party consultant was conducted to determine the optimum fracture design. The study concluded that, for various reasons, the fractures were conductivity-limited, and that larger proppant was needed to improve effective fracture conductivity. This recommendation was furthered by implementing ceramic proppant, a process discussed in detail in the complete paper.