The Meramec and Osage formations in the Anadarko basin are known to be tight rocks with low-matrix porosity and potentially minor or major fracture permeability. The Meramec is predominantly composed of clastic rocks and carbonates, while the Osage has a shallow limestone facies and a deeper mudstone with Chert facies. It is important to identify the location, frequency, size and type of fractures especially for identifying targets for landing points and for optimizing completions. These fractures could enhance or impede the production performance of the well.
While operators are used to deploying traditional techniques for identifying bore-hole fractures via post-drilling wire line logging runs, alternative techniques have been tested in recent years in various geological settings, especially in the unconventional wells. One of the methods recently tested and validated in conventional rocks is fracture detection while drilling, by means of surface measurements. This is made possible with the help of an advanced flow monitoring sensor, installed strategically on the drilling rig mud returns flow-line. The flow sensor, either a Coriolis or an Electromagnetic (EM) type, is capable of detecting micro-losses in the drilling fluid, by operating with high sensitivity and accuracy.
Applying an interpretational model to the derived observed micro-losses, enables the identification of open fractures, micro-fractures and induced fractures occurring with different apertures and densities. Real-time quantitative mud-gas provides valuable insight on whether the fractures are hydrocarbon bearing or not, while running X-ray fluorescence (XRF) on drilled cuttings can be used to complement and confirm the changes in lithology and correlate fractures with specific trace elements, which in-turn aids in anticipating a tight zone or a fluid-loss zone. The integration of fracture detection data, XRF and formation gas is combined with wireline log data to provide additional insights to differentiate conductive fractures from resistive fractures.
This paper outlines the details of this technique and its workflow which was implemented to characterize the reservoir sections in both the Meramec and the Osage formations in vertical and lateral wells drilled within the Anadarko basin and how this interpretation could subsequently aid in optimizing completions and production in future wells.