Prior to 1997, it was believed that propped fractures would not be successful due to excessive proppant embedment into the soft chalk. However, after three years of production, the first well receiving proppant produced 1 million barrels of incremental oil compared to acid-stimulated counterparts. Wells receiving propped fractures are expected to recover twice the oil reserves of acid-stimulated wells.
The Eldfisk oil field is a high-porosity, low-permeability reservoir of soft chalk in the Norwegian North Sea. Commercial oil production from the Eldfisk field is dependent on well stimulations. To date, pseudolimited-entry acid stimulation (PLEAS) has been the standard completion technique. This technique initiates relatively high (5,000 BOPD) individual-well oil-production rates. Over time, however, many of the Eldfisk wells have experienced rapidly declining oil production characterized by wellbore skin increase and fracture closure. Solids production and casing collapse have also been problematic. In late 1997, an alternative completion technique involving four hydraulic propped-fracture stages was successfully executed in an Eldfisk horizontal well. This paper presents a simple methodology to evaluate sustained productivity enhancement of propped fractures vs. acid stimulations in soft chalk formations based on the use of analytical modeling in combination with empirical production-data analysis.
Author(s): C.C. Cook, Norsk Hydro ASA; K. Brekke, PTI-Scandpower A/S
Paper Number: SPE 88031