Evaluation of a Fractured Tight Reservoir in Real-Time: The Importance of Detecting Open Fractures While Drilling With Accurate Mud Flow Measurement

Abstract

An advanced system of mud flow measurement while drilling enabled to detect fractures and intervals of high permeability within a tight, fractured reservoir via the identification and interpretation of mud micro-losses. The system is based on an electromagnetic flow meter installed on the flow line. The high accuracy of the flow data obtained was achieved thanks to the specifications of the meter, much more accurate than standard field systems, and with fit-for-purpose installation design of the system. Standard mud flow detection while drilling only enables a qualitative indication of the flow and it is not sensitive enough to identify subtle flow changes linked to the initial stages of an influx or to the minor fluid loss occurring when a formation fracture is encountered. However, the more direct, instantaneous indication of the presence of an open fracture in a well comes from the mud flow variations. The authors have utilized such data in conjunction with offset data from previous wells and existing literature, which indicated the presence of two different set of fractures with different aperture and density. An interpretation model was then generated and applied to the well being drilled. The fracture detection capability was enhanced by the analysis of drilling and hydraulic parameters variations also recorded in Real-Time; their change was related to change of the mechanical properties or the rock. Another decisive parameter monitored was the mud gas, since gas readings variations were often associated with the presence of open fractures in which hydrocarbons were circulating. The two families of fractures were clearly identified using this technique. The system and procedure have been recognised as a valid solution for fractured reservoir characterization and have been used in a composite log along with other data from e-logs, collected after the well was drilled. Furthermore the system enabled to detect the mechanical fractures induced by the drilling action, which masked the natural open fractures pattern in the e-logs of the offset wells drilled previously in the same basin.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015