Pineda, Wilson (BP) | Wadsworth, Jennifer (BP) | Halverson, Dann (BP) | Mathers, Genevive (BP) | Cedillo, Gerardo (BP) | Maeso, Carlos (Schlumberger) | Maggs, David (Schlumberger) | Watcharophat, Hathairat (Schlumberger) | Xu, Weixin (Wayne) (Schlumberger)
Deepwater depositional environments in the Gulf of Mexico can be very complex. Accurate determination of depositional facies is important in these capital-intensive fields. The most common reservoir facies are laterally extensive sheet sandstones with thin mudrock layers, channel complexes (isolated or amalgamated) and channel-levee complexes (often with poor reservoir communication). Reservoirs are often complicated by steep dips close to salt domes and the presence of potential fluid conduits due to faults or fractures. Borehole images aid in determining the character of the sediments, as well as improve net sand calculations, and illuminate the geology in the near wellbore region both in structure and depositional environment, and to provide valuable geomechanics information for the determination of the stress vector.
A well was recently drilled through one of these deep water sediment sequences in the Gulf of Mexico with an oil-based mud (OBM) system. An extensive acquisition program included a series of logging while drilling (LWD) and wireline images. In addition to the current LWD lower resolution borehole imaging tools, a new LWD dual physics OBM imager was deployed for the first time in this field. Five different types of physics were acquired, including lower-resolution images from nuclear measurements (gamma ray, density and photoelectric) and the high-resolution images from dualphysics OBM imager (DPOI) which is based on resistivity and ultrasonic measurements. Wireline high-resolution OBM resistivity images were also acquired. This paper shows a comparison of images collected with the new DPOI versus traditional LWD images and high-resolution wireline resistivity images.
Comparisons of the types of features observed from the various imaging tools were made, showing how the differences in physics, resolution and time of logging affects the images, as well as the impact these factors can have on subsequent interpretations. Four main categories of features are included in comparisons between the tools: sand-rich sections, consistently dipping mudrocks, chaotic zones and fractures/faults. The different images allow fuller interpretation of the gross sequence. In general, the higher the resolution, the more detailed and confident the interpretation is, particularly where the hole conditions are good. In degraded borehole sections, the LWD acquisition was beneficial for obtaining images as early as possible, when damage was at a minimum. The impact of the differences in the physics depends on the properties and contrasts being imaged. This is observed with fractures - both conductive and resistive examples can be seen on both LWD and wireline images. The ultrasonic images are complementary with both low and high amplitude fractures seen, providing more confidence in the fracture interpretation.
A new LWD ultrasonic imager for use in both water- and oil-based muds uses acoustic impedance contrast and ultrasonic amplitude measurements to obtain high-resolution structural, stratigraphic and borehole geometry information. Following extensive testing in the Middle East and the US, this paper presents results from the first European deployment of the new 4.75-in. high-resolution ultrasonic imaging tool.
An ultrasonic transducer, which operates at high frequency, scans the borehole at a high sampling rate to provide detailed measurements of amplitude and traveltime. A borehole caliper measurement is made, based on the time of arrival of the first reflection from the borehole wall. A second measurement detects formation features and tectonic stress indicators from the change in signal amplitude. The amplitude of the reflected wave is a function of the acoustic impedance of the medium. Resulting impedance maps have sufficient resolution to detect sinusoidal, non-sinusoidal and discontinuous features on the borehole wall.
Breakouts, drilling-induced fractures, and tensile zones were used for stress direction determination. Breakout identification was obtained both from amplitude images and oriented potato plot cross sections derived from traveltime measurements.
The orientation of natural fractures is parallel at the maximum stress direction, indicated by drilling-induced fractures and tensile zones. The World Stress Map confirms the maximum stress direction determination.
It was also possible to detect certain key-seat zones and investigate borehole conditions to prevent issues during the subsequent casing job.
The new LWD ultrasonic imaging technique represents an important alternative to density and water-based mud resistivity imaging, which has several limitations. Unlike the resistive imaging LWD tool that is very sensitive to standoff, the higher tolerance of the ultrasonic imaging tool enables the amplitude and traveltime ultrasonic images to contain fewer unwanted artifacts.
AL-Hassani, Sultan Dahi (ADNOC Offshore) | Ahmed, Shafiq Naseem (ADNOC Offshore) | Khan, Owais Ameer (ADNOC Offshore) | AL-Tameemi, Ibrahim Mohamed (ADNOC Offshore) | Khan, Shahnawaz (Schlumberger) | Marza, Philippe (Schlumberger) | Abdulrahim, Jaja Uruzula (Schlumberger) | Shasmal, Sudipan (Schlumberger) | Alexander, Malcolm (Schlumberger)
Reservoirs located offshore Abu Dhabi can be complex in terms of sub-seismic structural features such as faults and localized deformations. With use of high-resolution resistivity image logs, a TST (true stratigraphic thickness) technique, along with 3D structural models, uncertainties related to sub seismic structural ambiguities are resolved and well trajectory is optimized while drilling.
In this case study, real-time resistivity image logs were used while drilling. The sinusoid’s shape on images provided cutting down dip or up dip information. Dip trends were analyzed using a dip vector plot and to identify zones-of-interest. Dip attribute along with the log response were compared with the pre-job model and the inclination is adjusted accordingly during drilling. Several high angle features can be characterized as stratigraphic changes, fractures, or faults. The morphology and trend change observed in the dip vector plot of these features lead to the conclusion that these are sub-seismic resolution faults and deformation is associated with the fault.
The stratigraphic drilling polarity and the TST were calculated using the formation dip data. Using a TST scale and splitting the logs into stratigraphic drilling polarity domains, the fault throw displacement is estimated. The model is updated to reflect the interpreted data. The fault plunge and trend are extrapolated away from the wellbore and to nearby wells.
Summary Seismic While Drilling (SWD) is usually planned to acquire Real-Time (RT) seismic checkshot data during drilling to mitigate the risk related to depth uncertainty and target true location. The borehole seismic checkshot transit time may be determined using either "Break-to-Break" or "Trough-to-trough" timepick conventions. This case study shows how the choice of technique can have a significant impact on target depth predictions during SWD operations in an exploration well. In addition, a method is proposed on how to select the best technique to use for SWD depth prediction based on the available predrill data.
Equinor will use permanent reservoir monitoring (PRM) to help improve recovery in two of the operator's more important offshore projects of the next few years. The Norwegian state-owned operator has exercised an option in an existing framework agreement with Alcatel Submarine Networks (ASN) to implement the technology at its Johan Castberg field in the Barents Sea. That framework agreement was reached in January for PRM deployment at the Johan Sverdrup field in the North Sea. The technology involves the permanent installation of seismic sensors on the seabed, enabling the operator to continually monitor reservoir changes--with better images--throughout the lifespan of a field. Equinor said the information generated from PRM will aid its overall efforts in visualization, modeling, and, eventually, predictive analyses.
The Permian (Leonardian) Bone Spring Formation of the west Texas and southeastern New Mexico Delaware Basin (Figure 1) is one of the original targets of the unconventional resources boom. It comprises four major packages – the Avalon, and the First, Second, and Third Bone Spring units – and presents significant potential for stacked pay development (Figure 2). However, geologically and petrophysically these distinct units are difficult to understand and map with the basic log data routinely available.
In the Leonardian, basinal depositional processes dominated in the focus area of Loving, Ward, and Reeves counties, Texas, while slope and shelf deposits are found further to the east and west in Texas as well as northward in New Mexico (Silver and Todd, 1969; Gawloski, 1987; Saller et al., 1989; Montgomery, 1997; Allen et al., 2013; Nester et al., 2014). Turbiditic and mass flows pushed deep into the basin and deposited major submarine fan complexes. Conventional hydrocarbon accumulations are found proximal to the slope in channel sands/overbank deposits while distal silts in the focus area are unconventional with horizontal developments (Figure 3).
Within the study area, the Bone Spring is approximately 3000 feet of a complex, very heterogeneous succession of basinal turbiditic siltstones and shales intermixed with mass flow deposits and hemipelagics. The low resistivity turbiditic silts historically are the primary targets. The interbedded shales may be rich or lean in organic matter. Carbonate-rich layers – including diagenetically cemented silts – are common. This vertical and lateral heterogeneity adds interpretive complexity which is best addressed with conventional core. However, core is expensive to acquire and analyze, and the coring process adds to wellbore risk. Assessing changes in rock facies with advanced logs could be a cost-effective trade-off to full core acquisition.
Drilling risk can be migrated based on borehole failure mechanism analysis, which provides valuable information for wellbore stability and formation damage protection. It is very challenging to identify the borehole failure in oilbase mud environment because of lacking of high resolution borehole image although we can get some information from cutting shape or sonic data with high uncertainty.
A new photorealistic micro-electrical imager for oil-based mud provides rich information on borehole failure and related formation damage from 3 different images (resistivity, permittivity and stand-off). The different borehole failure mode including tensile, compressional or shear are easily identified from resistivity or permittivity image.
The multiple arm radius data of this imager was also used to for borehole failure identification complementing with image feature interpretation. The special stand-off image was integrated for borehole failure identification as well.
One case study from Clair field, west of Shetlands North Sea was presented to demonstrate the borehole failure identification. The horizontal incipient breakout in horizontal well provides the consistent extensional stress regime; the breakout from vertical well show the new understanding of minimum horizontal stress and the mixture of drilling induced fracture and incipient breakout indicate the small ratio of two horizontal stress. The one dimensional mechanical earth model (MEM) of a horizontal well was updated based on borehole failure mechanism. The new MEM is more consistent with field leak of testing in other wells and provide valuable information for mud optimization to improve drilling efficiency in different risk intervals.
The new high-definition OBM-adapted micro-electrical imagesenabled confident identification and quantification of borehole tensile orshear failures and provides direct evidence for single well geomechanics earth model calibration.
Hachino, Y. (Earth Scanning Association) | Yasutomi, H. (Earth Scanning Association) | K. Tajima, K. (Earth Scanning Association) | Ootsuka, Y. (Earth Scanning Association) | Wada, T. (RaaX Co. Ltd.) | Aydan, Ö. (University of the Ryukyus)
ABSTRACT: In the soil improvement by mechanical stirring, an improved pile is made by stirring cement milk and local soil using characteristic blades in the underground.In order to get the improved pile which satisfies high quality and predetermined compressive strength, it becomes a big issue to make a homogeneous improved pile and to evaluate mechanical properties of the improved pile quickly in the field.Mechanical properties of an improved pile are affected by the solid portion (matrix mixed by cement milk and local soil) and the unsolid portion (unmixed void). Therefore, mechanical evaluation as a composite material is needed to verify the quality of an improved pile. In this study, Authors introduce a method due to stereology to estimate the total volume of the unsolid portion from the borehole wall imaging of borehole televiewer. Authors take a couple of homogenization mechanical models (mixture model, micro-structure model) which are assumed from the result. Finally, Authors propose the empirical formula related to homogenized physical properties of the improved body.
A field experiment was performed on a ground improvement pile made of heterogeneous materials, using an ultrasonic scanner (USS).
Authors hereby report that the experiment demonstrated that it may be possible to evaluate the physical properties of bedrock using ultrasonic wave reflection intensity.
2 SPECIFICATIONS OF MEASURING EQUIPMENT INSIDE THE BOREHOLE
The devices Authors used for the imaging and ultrasonic wave reflection intensity measurement in a borehole during this study were an optical digital scanner (ODS), an ultrasonic scanner (USS), and a full wave system (FWS).
The ODS is an optical camera to take borehole wall images from a constant azimuth. The USS is a system which revolves an ultrasonic wave oscillator and receiver in a spiral manner to continuously measure the ultrasonic wave reflection intensity of the borehole wall and obtains borehole wall images by converting the intensity into 256-tone color density. The FWS is a system which applies ultrasonic waves to a point on a borehole wall, obtains waveform data from the reflection, and measures the maximum reflection intensity of that point directly from the waveform. Figure 1 is a conceptual view of how the three systems acquire data.
Weatherford introduced the compact oil-based-mud (OBM) microimager (COI), a slim-profile tool that delivers fullbore, high-definition images in wells drilled with oil-, diesel-, or synthetic-based muds. The COI features eight pads with 72 total measurement electrodes that provide optimum coverage. The images can be enhanced further through Weatherford Reveal 360 image processing. Through analysis of the COI images, the structural, stratigraphic, and depositional geology around the wellbore can be detailed, even in wells previously deemed too complex for imaging services. Recently, the COI was deployed with other petrophysical-measurement tools in an 8¾-in.
IntroductionAs the number of wells drilled in the Utica Shale play continues to grow, maximizing well performance by optimizing wellbore orientation, landing point and proper completion strategy are vital to the success of this play. This paper will focus on wellbore orientation. Most of the wellbores drilled in the Ordovician Point Pleasant member of the Lower Utica Formation, the target landing zone in the play, have used an orientation similar to the shallower Devonian Marcellus wells (Figure 1). In the Marcellus, this orientation is used to improve the effectiveness of the fracturing process by exploiting the in-situ rock stress. Orienting the wellbore properly with respect to the principal horizontal stress direction helps to keep the fractures induced by the hydraulic fracturing process from closing. In the Devonian Marcellus play, deviating from the preferred wellbore orientation negatively impacts well production. Wellbore image data, sonic anisotropy, and microseismic are tools used to determine the direction of the principal stress and in turn, the orientation of the horizontal wellbore.