The presentation “A METHOD TO IDENTIFY VERTICAL RESERVOIR PRESSURE COMMUNICATION BY COMBINING BOREHOLE SONIC AND HIGH-FREQUENCY ELECTRICAL IMAGING DATA” will be given by Knut Arne Birkeland, from Aker BP and Harish B. Datir, from SLB.
Natural fractures and faults result from the tectonic and structural history of rock formations. While laterally extensive fracture networks can increase the depletion area, they can create challenges due to fluid channelling-pressure communication. Electrical imaging is used at the wellbore to identify fractures/faults. However, interpreting open features is difficult in oil-based mud (OBM) as they can appear resistive. Ultrasonic images lose sensitivity in the presence of spirals, drill marks, or non-homogeneous mud. The borehole acoustic imaging uses 3-dimensional slowness time coherence and ray tracing to determine far-field reflectors, providing acoustic reflectors dip/azimuth and their distance away from wellbore. Combining these two it can provide a reflectors map of fractures and faults but cannot confirm their openness. To address this, we present a method that uses Hayman image to assist analyzing open fractures/faults. Correlating the wellbore fracture/fault planes with 3D slowness time coherence and ray tracing (sonic far field) based event, we interpreted the extension of fractures and faults from the wellbore into the formation on surface seismic aligned section and identified potential pressure communication channels.
In OBM, MHz frequency imager data can produce resistivity, dielectric permittivity, and standoff images through advanced inversion processing. By combining dielectric and resistivity information, a new Hayman image can be generated through post-processing. Jointly analyzing resistivity and Hayman images helps resolve open/partially open features even when borehole rugosity is high, and other imaging techniques lose sensitivity. Mapping these identified fractures/faults and interpreted potentially unstable fractures away from the wellbore wall helped in identifying the orientations and alignments of the wellbore and far-field events on surface seismic aligned sonic migrated image.
A joint interpretation of resistivity and Hayman images (pilot well) identified two additional open/partially open fractures in the upper-middle section, along with several closed fractures and two closed faults. In the middle of the well there is a depth interval where closed fracture density increases compared to above and below. This interval is identified as an unstable zone from the borehole image. Comparing with the far field sonic processed results, this unstable interval has the highest density of sonic reflectors. The azimuth of the open fractures interpreted from the image upper section is in alignment with a side-track well open fractures interpreted in the unstable zone.
In this case study, we identified open and unstable closed fractures intervals that extend into the formation and can form a pressure communication channel when the well is put into injection. These observations were consistent with field pressure communication and substantiated with production logging measurements. This spatially resolved fracture network is essential for subsurface understanding and future well placement in this field, providing critical input for the dynamic reservoir model.
Knut Arne Birkedal is a Sr. Petrophysicist in AkerBP. He joined ConocoPhillips in 2013 as a Reservoir Engineer, and AkerBP in 2018. He has a MSc and PhD in Reservoir Physics from the University of Bergen and was also a Fulbright Scholar at Lawrence Berkeley National Laboratory. His interests include gas hydrates, EOR, core studies and modeling.
Harish B. Datir is a Petrophysics and Geology Domain Champion, based in Stavanger, Norway. He joined slb in 2007 as a Wireline Field Engineer in Saudi Arabia. Since then, he has taken different roles in different locations before taking on his current position as Wireline Domain Champion. He has worked in the Middle East for four years, and for the past twelve years, he has been working in Scandinavia, covering mainly Norway and Denmark operations. He has a BS degree in applied geology and a master’s degree in applied geophysics. His work focuses on developing integrated petrophysical answer products and improving the existing ones in support to increase utilization of Schlumberger log measurements.