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Lampiran Gambar1:
Figure 1. BJP-1 lithology, formations, casing points, and available petrophysical data, as well as available petrophysical data from the Wunut Field and Porong-1 well, all located within 7 km of the Lusi mud volcano (original data sourced from Kusumastuti et al., 2000, 2002; Lapindo and Schlumberger, 2006; Mazzini et al., 2007; Istadi et al., 2009, 2012; Sawolo et al., 2009; Tanikawa et al., 2010; Lupi et al., 2014). All depths are in meters true vertical depth relative to the rotary table. Petrophysical data have been carefully processed, checked, and corrected for significant errors caused by the poor logging conditions (see the caliper log).
Density data have been estimated for some sections from P-wave velocity data, as per the Gardner et al. (1974) relationship, and they provide a good match to measured data from BJP-1 and offset wells. Shallow S-wave sonic slowness data have been estimated using the
Castagna et al. (1985) method, Lee (2010) method, and by fuzzy logic and genetic algorithm methods (Rajabi et al., 2010), and they provide a reliable match to measured S-wave data. Porosity estimates from sonic, density, and corrected neutron porosity log data all yield consistent results and suggest that the shales have relatively constant porosities (35%–45%) with depth, and the volcanic sequences have very low porosities (2%–10%).
Figure 2. East–west 2D reflection seismic section (modified after Mazzini et al.,2007) with the author’s interpretation (the two-way time is in seconds; the key reflectors are dashed where inferred due to low seismic quality). Seismic quality is generally poor, particularly near the BJP-1 drilling site. In particular, note the lack of any noticeable difference in seismic character from the volcanic sequences, which trend into Lower Kalibeng clays and silts toward the Porong-1 well, 7 km to the east (just off of the seismic section). Furthermore, there is a notable absence of any significant or continuous seismic reflectors visible in the shallow sequences above the Kalibeng clays in the immediate vicinity of the BJP-1 well.
This is consistent with the absence of any major P- or S-wave velocity contrasts in the petrophysical and check-shot velocity data (Figure 1). Listed depths are at the BJP-1 well location, and all reflector two-way times are verified from BJP-1 check-shot data.
Table 1. Timing of key events during drilling of BJP-1. All dates and times are local (UTC .7 h). Significant observations and interpretations are italicized in bold. Data are compiled from Adams (2006), Davies et al. (2008, 2010), Tingay et al. (2008), and Sawolo et al. (2009).
Figure 3. (a) Previously published velocity data for BJP-1, check-shot velocity
data, raw field-processed sonic log data, and the final carefully processed and corrected compressional sonic velocity data presented herein. (b) BJP-1 casing points, formations, and lithologies. (c) Caliper log data from BJP-1. (d) BJP-1 measured S-wave slowness (DTS) and consistent estimates of shallow DTS made using four different methods. Previously published sonic velocity data (Lapindo and Schlumberger, 2006; Istadi et al., 2009, 2012; Lupi et al., 2013, 2014) contain numerous errors and artifacts for the entire length of the BJP-1 wellbore. Errors include inclusion of casing velocities, high- and low-velocity acquisition artifacts caused by borehole rugosity and breakout, and artifacts generated by improper, rapid, or unchecked processing. All previously published velocity models are spurious and unreliable and should not be used for any studies on the Lusi mud volcano.
Figure 4. Compilation of all available pore pressure information from the BJP-1 well, as well as the nearby Wunut Field and Porong-1 well and previously published predrill and postdrill pore pressure predictions (data sourced from Kusumastuti et al., 2000, 2002; Lapindo and Schlumberger, 2006; Davies et al., 2007, 2008; Mazzini et al., 2007; Tingay et al., 2008; Istadi et al., 2009, 2012; Sawolo et al., 2009; Tanikawa et al., 2010). All pressure gradients are in MPa∕km (or kPa∕m), and depths are in meters true vertical depth relative to the rotary table (11.2 m above ground level). Where possible, unpublished original data have been verified against secondary data, checked for accuracy, and confirmed by reliable published or reported values. Note that Porong-1 appears to have slightly lower pore pressures in the Pucangan and Kalibeng clay sequences than observed in BJP-1 and Wunut, based on WFITs, lower leak-off pressures, slightly faster compressional velocity, and higher resistivity (Figure 1).
Acknowledgments
I wish to thank B. Istadi and R. Sawolo for many valuable discussions on the Lusi mud volcano and the BJP-1 well.
In particular, I wish to thank B. Istadi for providing access to data that have been used to confirm and validate the reported and published data used herein, as well as for his efforts to help correct and reprocess erroneous published petrophysical log data from BJP1.
I also wish to thank M. Rudolph for his advice and help in understanding key aspects related to longevity prediction of the Lusi mud volcano, help in digitizing published log data, as well as insights into models examining the potential for earthquake triggering of Lusi.
M. Rajabi is thanked for providing BJP-1 S-wave velocity estimates using fuzzy logic and genetic algorithm methods. I wish to thank K. Boyle, D. Fischer, and an anonymous petrophysicist at Energi Mega Persada for providing resources, literature, help, and valuable discussions on the identification and correction of errors and artifacts in BJP-1 petrophysical data. Finally, I would like to thank the associate editor K. Bradford and two anonymous reviewers for providing valuable and insightful feedback on the manuscript.
BIODATA MARK TINGAY
Mark Tingay has more than 13 years of experience in overpressure analysis, pore pressure prediction, and petroleumgeomechanics.
He graduated with a Ph.D. from the University of Adelaide in 2003 with a thesis entitled “In situ stress and overpressures of Brunei Darussalam.” Since 2003, he has conducted more than 20 industry-based research and consulting projects on a range of petroleum geomechanics and overpressure issues.
Tingay has worked worldwide, but with a primary focus on the Asia-Pacific region, including compilation of the first present-day stress map for Southeast Asian petroleum basins; determination of overpressure origins in Brunei, Thailand, and Malaysia; and new pore pressure prediction methods for the Gulf of Thailand and Northwest Borneo. His research includes publication of more than 50 peer-reviewed papers; giving more than 100 presentations to conferences, professional society meetings and companies; and providing more than 80 media interviews. Since 2013, he has had the combined roles of rock
mechanics research scientist at Chevron and adjunct associate professor in geomechanics and drilling engineering at the University of Adelaide.