Unconventional wells have been known to revolutionize the oil and gas industry in the last decade. The downhole diagnostics play an essential part in understanding the well completion and reservoir performance. Main objectives for the downhole surveys can include:
– Assessment of the inflow intervals.
– Assessment of zonal isolation and failures resulted in the communication of the stimulated zones
– Assessment of induced fractures, their initiation points and heights.
– Completion performance and its integrity.
– Location of zones producing unwanted water or gas.
– In the complex completion design, independent analysis of the wellbore, annular, and reservoir flows.
To target the objectives, operators usually perform downhole production logging (PL) surveys including array spinners; utilize downhole distributed temperature and acoustic sensors (DTS/DAS), tracers etc. But even in case the good data quality, the acquired datasets do not provide the complete answer due to the following limitations:
– Scanning of the wellbore flow only.
– High thresholds for flow rate and composition.
– Classification of the flow type and its path inside and outside the casing or liner.
– Qualitative assessment of DTS / DAS data, especially in the case of multiphase flow.
The above requirements for the downhole assessment led to the development of new data acquisition methods, hardware and software to enable quantification and classification of the inflow with an extended scanning radius.
The paper will discuss the concept and principles of downhole scanning using high precision temperature and spectral acoustic logging, its evolution and implementation in unconventional reservoirs, which helped the operator to evaluate the efficiency of multistage hydraulic fracturing by evaluating key control parameters.
Efficient development of a low-permeability unconventional plays requires stimulation. Most of operators stimulate to create a network of small fractures in a significant volume in unconventional reservoir, which plays the role of a drainage area with artificial fracturing (well-known as Stimulated Reservoir Volume or SRV). To assess the effectiveness of hydraulic fracturing or identify SRV efficiency, it is important to determine whether a single planar fracture, or a network of small fractures, has been created by stimulation. Accurate diagnostics of SRV gives operator an important piece of information to improve stimulation technique for a given unconventional reservoir condition.