MODERN AZIMUTHAL RESISTIVITY TOOLS AND THEIR APPLICATION TO MATURE FIELD DEVELOPMENT

Transcription

1 MODERN AZIMUTHAL RESISTIVITY TOOLS AND THEIR APPLICATION TO MATURE FIELD DEVELOPMENT Mike Dautel, Jason Pitcher, and Michael Bittar, Halliburton Copyright 2011, held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors. This paper was prepared for presentation at the SPWLA-INDIA 3rd Annual Logging Symposium, Mumbai, India Nov 25-26, ABSTRACT Mature field development often requires a new look at the technology used for development. In the early stages of the lifecycle of a field, many logs are acquired to assist operators in the creation of development strategies and in understanding the ongoing development of the field. As the field matures, data acquisition programs are scaled back to a minimum while the easiest, most accessible targets are produced. In the later stages of the development, operators elect to re-examine the field areas in which new technology, such as azimuthal resistivity, can assist in gaining access to bypassed reserves and to thin bed areas that were originally not thought to be practical development targets. This paper presents a review of azimuthal resistivity tools and their theory of operation. It includes a discussion of the use of modeling, as well as a synopsis of methods used to determine the depth of detection and measurement for the various potential measurements made by these tools. Finally, the paper describes two case histories that illustrate the use of azimuthal resistivity tools in mature fields to access bypassed reserves. Geologically complex environments are examined from the perspective of using the new measurements to obtain better geological and petrophysical answers. Thin bed environments are examined with these measurements to obtain a better understanding of development possibilities than was previously possible with the use of wave propagation resistivity tools INTRODUCTION In oilfield exploration, logging tools are used in a borehole to measure the surrounding earth parameters by producing a log recorded as a function of depth or position of the tool in the borehole and presenting geology information of the underground structures. Obtaining knowledge of geologic formations downhole helps to further increase oil production in the reservoir. With the decline of oil discoveries, reservoir management efforts aimed at maximizing production through optimal wellbore placement require increasingly sophisticated geosteering and formation evaluation capabilities. Drilling through complex reservoirs with traditional technology is difficult because pre-well geological models are often limited to the resolution of seismic data. Effective schemes for reservoir drainage to maximize net recovery focus on increased production, optimized production, reduced cost, better reserves estimates, and accessing more reserves. The means of accomplishing this objective is two-fold: improve reservoir understanding and create effective schemes for reservoir drainage to maximize net recovery by maximizing reservoir contact. A new azimuthal deep resistivity (ADR ) logging-while-drilling sensor accomplishes this objective. The tool is designed to combine a deep reading azimuthal (directional) measurement and petrophysical interpretation capabilities in a two-in-one geosteering/formation evaluation service. The ADR tool provides a deep reading azimuthal (directional) service that greatly enhances geosteering and provides significantly greater well placement control when drilling horizontal wells. The system also provides important petrophysical parameters, such as the horizontal resistivity, Rh, the vertical resistivity, Rv, and the relative dip angle. 1

2 For the drillers and geologists, this system provides the capability to steer the well through the most productive part of the oil or gas reservoir while maintaining a desired distance from the overlying formation. The sensor is based on electromagnetic propagation and can detect boundaries up to 18 ft from the wellbore. Because of its azimuthal capability, the sensor can also help determine the azimuth of an approaching boundary and image a formation several feet away from the wellbore (Bittar 2002; Bittar et al. 2007). This functionality was a critical factor in the recent successful placement of a horizontal well section in a thin reservoir in mature fields. REVIEW OF AZIMUTHAL RESISTIVITY TOOLS The ADR sensor, shown in Fig. 1, is based on the tilted antenna concept and features multiple spacing and multiple frequencies. The sensor operates at three different frequencies (2 MHz, 500 khz, and 125 khz) and consists of six coaxial transmitters and three tilted receivers with transmitter-to-receiver distances spanning from 16 to 112 in. The receivers antennas are tilted 45 degrees with respect to the tool axis. Fig. 1 The azimuthal deep resistivity sensor. By using multiple spacings and multiple operating frequencies, the ADR sensor maps the near-wellbore properties from shallow depth to deep into the formation. The longer spacing and lower frequencies are used to measure the formation properties of the uninvaded zone. With three operating frequencies of 2 MHz, 500 khz, and 125 khz, the sensor retains the advantages of high frequency data, such as greater accuracy in high resistivities and better vertical resolution, while gaining the advantages of the lower frequency measurements, including significantly greater depths of investigation, thus sensing the bed boundaries around the borehole up to 18 ft away (Bittar et al. 2008; Bittar et al. 2010). As the tool rotates, phase shift and attenuation measurements are acquired in 32 azimuthally oriented bins (Fig. 2) referenced to either the high side of the borehole or magnetic north using magnetometers. The phase shift and attenuation measurements are transformed to resistivity to obtain 32 azimuthally oriented phase shift and attenuation resistivities at multiple spacing and frequencies. Fig. 2 Data acquired in 32 azimuthal bins. 2

3 GEOSIGNAL MEASUREMENT Traditional logging-while-drilling (LWD) wave propagation exhibits polarization horns as the tool approached bed boundaries. Fig. 3 shows the computed response of a traditional LWD wave propagation tool in a payzone of 10 ohm-m that is between two conductive shale beds of 1 ohm-m. As the tool approaches the resistive bed from the bottom, the tool is affected by polarization effects and reads high resistivity; as the tool approaches the bottom conductive shale, the tool also begins to read high resistivity (same polarization effect). The tool reading is the same as the tool approaches the conductive shale from the top or the bottom. This similarity is attributable to the lack of azimuthal sensitivity, thus making geosteering in the payzone unpredictable and uncertain. 1 ohm-m 10 ohm-m Well Trajectory 1 ohm-m Polarization Horn Polarization Horn Fig. 3 Response of a traditional LWD wave propagation tool. The azimuthal deep reading resistivity tool also provides a new type of directional measurement: the geosignal. The geosignal is a difference between measurements (phase or attenuation) determined at opposite azimuthal orientations of the tool. The directional geosignal decreases as the tool approaches the conductive boundary from the bottom of the payzone and increases as the tool approaches the conductive boundary from the top of the payzone. Fig. 4 shows the computed response of a geosignal in a payzone of 10 ohm-m that is between two conductive shale beds of 1 ohm-m. As the tool approaches the conductive shale from the bottom, the geosignal exhibits a negative polarity; as the tool approaches the conductive shale from the top, the geosignal exhibits a positive polarity. This directional sensitivity can be exploited in making geosteering in the payzone predictable and more certain. 3

4 1 ohm-m 10 ohm-m Well Trajectory 1 ohm-m (+ve) (-ve) Fig. 4 Geosignal response of the azimuthal deep reading resistivity tool. RESISTIVITY MEASUREMENT AND MODELING For the petrophysicist, the resistivity of the formation is essential in the evaluation of the amount and type of fluid found in the pore spaces of the reservoirs. Resistivity measurements can provide indications of hydrocarbon concentrations and other information useful to petrophysicists and reservoir engineers. However, such measurements can exhibit boundary-related artifacts that make interpretation difficult, particularly in situations in which the borehole penetrates the formations at a high angle. The ADR tool does not suffer the same problem because so many azimuthal measurements are made around the borehole. Thinly laminated sand-shale sequences can exhibit microscopic or macroscopic anisotropy. Microscopic anisotropy manifests in the orientation of the clay minerals in the shale. Macroscopic anisotropy can occur in a sequence of laminations of shale and sand. Traditional propagation tools have some response to anisotropy at high deviation. However, with transmitters and receivers oriented in a non-parallel plane, the ADR tool exhibits a very good response to anisotropy. Fig. 5 shows a modeled response of the ADR tool in an anisotropic formation for three different spacings: 16 in., 32 in., and 48 in. The frequency is 500 khz, Rh of 1 ohm-m, and Rv of 4 ohm-m. Fig. 6 shows a modeled response of the ADR tool in an anisotropic formation for three different frequencies: 2 MHz, 500 khz, and 125 khz. The transmitter/receiver spacing is 32 in. The horizontal resistivity, R h, is equal to 1 ohm-m; vertical resistivity, R v, is equal to 4 ohm-m. Using multi-spacing and multi-frequency azimuthal data, fast and robust inversion algorithms are developed to simultaneously determine the horizontal resistivity, R h, vertical resistivity, R v, and relative dip angle, corrected for shoulder and invasion effects. 4

5 Resistivity Resistivity SPWLA-INDIA 3rd Annual Logging Symposium, Mumbai, India Nov 25-26, different spacings; same frequency Anisotropic formation; Rh = 1 ohm-m; Rv = 4.0 ohm-m T khz T khz T khz Rotation angle Fig. 5 Tool response in anisotropic formation for three different spacings and same frequency different frequencies; same spacing Anisotropic formation; Rh = 1 ohm-m; Rv = 4.0 ohm-m T32 2MHz T32 1MHz T khz Rotation angle Fig. 6 Tool response in anisotropic formation for three different frequencies and same spacing. CASE HISTORIES The first case history is from California, USA. The Wilmington field, in production since 1932, is the largest field in the Los Angeles basin and the third largest oil field in the United States (Mayuga 1968). The Wilmington structure is a northwest-southeast trending, double plunging asymmetric anticline that is 13 miles long and up to 3 miles wide (Fig. 7). A series of transverse, normal faults segment the structure into 10 major productive fault blocks. Throughout the field, seven major producing zones, ranging in age from lower Pliocene to upper Miocene, have produced 2.6 billion bbl of oil and 326 BCF of associated gas from 6,000 wells. The field has an original oil in place reserve in excess of 10 billion bbl, with an estimated ultimate recovery of more than 3 billion bbl (Clarke and Henderson 1987). 5

6 Fig. 7 WTU-NWU location map and Wilmington anticline regional structure map (from Pitcher et al. 2009). The Wilmington productive section, has a gross thickness of approximately 3,000 ft; it comprises an aggradational succession of Miocene and Pliocene age confined slope deposits prograding into unconfined basinal medial to distal turbidite fan complexes. Medium- to thick-bedded hemipelagic mudstones separate successive lower slope, medial, and distal fan sand bodies. At the parasequence level, lithofacies comprise indurated mudstones, shales, and siltstones interbedded with semi-consolidated and unconsolidated fine- to coarse-grained sandstones. The optimal positioning of a complex well in a thinly laminated reservoir that has already been produced required careful planning on the part of the asset team. The objective was to use a low angle trajectory to assess the potential for waterflooding in the lower zones of the reservoir that could negaively affect production. The goal was to determine the relative prescence or absence of water before fully penetrating the lowest zone, which had the highest risk of waterflood. Fig. 8 shows the proposed plan in section. Blue=Top Octant Resistivity (Model) Brown =Bottom Octant Resistivity (Model) Red=48 500Khz Phase Resistivity (Model) Black =16 2Mhz Phase Resistivity (Model) Gamma Ray (Psudolog) Well Plan Fig. 8 Prewell proposed section (from Pitcher et al. 2009). 6

7 After entry into the lower zone, the resistivity values from the bottom octant indicated that water was not present in this lower zone to the detection limit of the tool. As the section was traversed, the measurement continued to indicate the absence of water, enabling the team to confidently drill the section (Fig. 9). Blue=Top Octant Resistivity Brown =Bottom Octant Resistivity Red=48 500Khz Phase Resistivity Black =16 2Mhz Phase Resistivity Gamma Ray Entry into lower unit Wellpath Fig. 9 Final drilled section (from Pitcher et al. 2009). WATER SATURATION FROM AZIMUTHAL RESISTIVITY Well 1 was drilled through the section and logged while-drilling with gamma ray and azimuthal resistivity (Fig. 10). The azimuthal resistivity measurement selected for the water saturation analysis was the 16-in. 500 khz phase measurement. This measurement was selected because of the relative insensitivity of the measurement to polarization effects and the need for maximum axial resolution to best define thin beds. The log shows the top octant, bottom octant, and the average resistivity measurements. The average measurement is insensitive to boundary effects and, in thinly bedded zones, should provide a measurement much closer to R t for the saturation calculation. Polarization effects from macro-anisotropy strongly affect the top and bottom octant resistivities, but have a very small influence on the average resistivity measurement. This finding fits well with the predicted results from the tool theory previously described. A major benefit of having the top and bottom octant resistivity is that the average resistivity can be qualified. If R top =R ave =R bottom, then R ave is unaffected by macro anisotropy. Even in areas where macro-anisotropy is evident, Rave can still be regarded as a reasonable measurement. The key to identifying an invalid Rave value is when the value of R top = R ave R bottom or when the value of R top R ave = R bottom. In this particular section, there are very few instances of invalid values of R ave based on the previously described rules, but this becomes a qualifying feature in horizontal holes. 7

8 Fig. 10 Well 1 log and water saturation comparison log (from Pitcher et al. 2009).. The saturation calculation was conventional using the specified constants. The results were calculated for each of the resistivities plotted. Fig. 10 shows the results of the analysis applied to the curves with Sw plotted for each. Polarization effects from macro-anisotropy strongly affect the top and bottom octant resistivities, but have a very small influence on the average resistivity measurement. This finding fits well with the predicted results from the tool theory previously described. The net-pay for the section was previously defined with a cutoff value of 80% Sw. The saturation data from the log was analyzed to determine the total net-pay through the section. The results are presented in Table 1. TABLE 1 - NET PAY FROM EACH RESISTIVITY MEASUREMENT (FROM PITCHER ET AL. 2009). Resistivity Measurement Ft Net-pay % Net-pay Sw from Ave <80% = Swe from Up <80%= Swe from down <80%= The use of an azimuthal resistivity tool that provides accurate compensated resistivity measurements around the borehole enabled the operator to make proactive decisions about drilling the well in real-time, before events such as waterflood zones are encountered. This was performed in a geologically challenging environment that does not lend itself to more simplistic tools. In addition to the well placement aspects, the ability to measure formation resistivity with little interference from macro-anisotropy significantly enhanced the operator s ability to confidently determine net pay. With omni-directional tools, the deepest reading resistivity was typically used as the input to a water saturation model because of the need to overcome invasion profiles. With LWD resistivity measurements, the formation has much less time to develop an invasion profile, enabling shorter spacings to be used. The issue with using long or short spacing sensors in thinly bedded rocks is macro-anisotropy, which is difficult to compensate for or quantify. The new azimuthal resistivity sensor enables the short spacing low frequency measurement to be qualified for use in water saturation modeling. The second example is from a field in Alaska, USA. Although the primary purpose of running an azimuthal resistivity tool is to geosteer the well (Pitcher et al. 2011), the tool also yields valuable petrophysical information in thin reservoirs and compensates for boundary effects in reservoir models. 8

9 Fig. 11 Practical log curves for geosteering (from Pitcher et al. 2011). Fig. 11 shows a field example. The lateral well in the example was rotary steerable drilled with a in. bit using a seawater gel mud system with a Rm at BHT of 0.17 ohm-m. Fig. 12 shows the borehole correction chart for the shallowest reading curve, the 16-in. 2 MHz phase shift curve. The chart shows that any borehole effect for this lateral is negligible for an in-gauge hole. 9

10 Fig. 12 Borehole correction chart for the 16-in. 2 MHz phase shift resistivity curve in a in. borehole (from Pitcher et al. 2011). Fig. 13 shows the memory data recorded while drilling the lateral. Track 1 displays the average gamma ray curve, which is shaded based on the gamma ray value. It also contains a true vertical depth curve that shows the well profile. The gamma ray and TVD curves show that the well was steered down section to a close approach to the bottom contact. The well was then steered up and out of zone through the gradational boundary at the top of the reservoir. The well was steered back down through the gradational boundary at the top of the reservoir and back into zone. At xx100 ft, it was decided to steer down through the bottom of the reservoir to confirm an unexpected reservoir thickness. Track 2 contains compensated 16-in. 2 MHz phase shift resistivity data. It presents the up and down resistivity curves and the average resistivity curve. Track 2 also contains a composite resistivity curve; the construction of this curve is described below. This curve has been offset by one cycle in the logarithmic plot. Track 3 contains compensated 48-in. 500 khz resistivity curves and shows the up and down resistivity curves and the average resistivity curve. Track 4 contains a highside oriented density image to aid in the interpretation of some resistivity effects related to discontinuous siderite layers in the reservoir. Because the gamma ray and resistivity curves were acquired on two tool runs while drilling, the formation exposure time was low. The density image was acquired on the last run. The image from the casing shoe to xx100 ft sensor depth was acquired while reaming to bottom and the section below while drilling. The reaming image shows the sand to be in-gauge after being open for approximately two days before density logging. The upper shale section from xx820 to xx910 ft shows some borehole breakout related to the two-day exposure time of this section before the density image was acquired. Using resistivity modeling as a guide, a composite resistivity curve was produced from the 16-in. 2 MHz resistivity curves. Casing was set at the top of the upper gradational boundary, as shown in Fig. 11. The resistivity curves follow the model fairly well below casing to the close approach of the base of the reservoir. Note the polarization horn on the 48-in. 500 khz top resistivity curve as the casing is exited, which is predicted by the model. The 16-in. 2 MHz model predicts that the 16-in. bottom curve will be the closest to the true resistivity value over the transition zone. The field data shows the top, bottom, and the average resistivity curves reading almost the same until xx450 ft. 10

11 The 16-in. 2MHz average curve was used in the composite over this section. At this point, some slight separation occurred that was likely caused by some thin siderite layers in this section of borehole. At xx475 ft, the 48-in. 500 khz data shows the curve separation predicted in the model as the base of the reservoir is approached. The base is not detected by the 16-in. 2 MHz data until xx510 ft, which is consistent with the modeling. The polarization horns on the top resistivity curves and the dip in the resistivity on the bottom resistivity curves for both the 16-in. 2 MHz and 48-in. 500 khz data appear as in the model. The model predicts that the average curves, though reading slightly less than the true resistivity, will be the closest to the formation resistivity at that TVD. The field data shows this for the 16-in. 2 MHz average curve, but the 48-in. 500 khz average curve shows a large polarization horn. It is possible that the actual wellbore is slightly nearer the boundary than the model, resulting in a larger polarization horn. An additional complication is that the wellbore skimmed off of a siderite layer in the bottom of the borehole. This skimming of the siderite layer could be the reason that the 16-in. 2 MHz average resistivity curve has the sharp increase in resistivity at xx575 ft that was not predicted by the model. Because this siderite layer is not continuous around the borehole and the majority of the borehole was in sand, it was decided to interpolate the 16-in. 2 MHz average resistivity curve from xx550 ft to xx597 ft, rather than the use the actual 16-in. 2 MHz data over this interval. The 16-in. 2 MHz average resistivity curve is carried in the composite resistivity curve until xx710 ft. The model predicts the separation of the 16-in. 2 MHz curves as the transition zone at the top of the reservoir is approached and drilled through. The 16-in. 2 MHz bottom resistivity curve is used in the composite curve from xx710 ft to xx990 ft. Note the effect of the thin dense siderite layers on the resistivity curves. The character of these spikes correlates well with the density data. At xx990 ft, the 16-in. 2 MHz average curve is used again for the composite. A bit trip was made when the sensor was at xx150 ft. After the bit trip, the sensor did not log a new hole until xx210 ft. This interval from xx150 ft to xx210 ft shows to be over gauge on the density image. The modeling did not compute the resistivity response for the wellbore drilling out of the base of the reservoir, as in the field example; it was expected, however, that the top resistivity would polarize, which was observed in the field data. The 16-in. 2 MHz average resistivity was selected for the composite resistivity curve to the end of the field example. 11

12 Fig. 13 Memory data plot for the lateral with a composite resistivity curve (from Pitcher et al. 2011). 12

13 CONCLUSIONS Mature fields present many challenges for successful development. It becomes necessary to access and drain bypassed sections of the reservoir that may be thinner and geologically more complex than those produced in the early stages of the life of the field. Optimal wellbore placement is crucial to maximize production rates and ultimate recovery volumes and to avoid premature water breakthrough. Proactive geosteering is key to achieving these objectives. Azimuthal deep reading resistivity tools provide the real-time measurements necessary to detect bed boundaries and fluid contacts, and to place the wellbore in the optimum position with respect to them. Formation evaluation is also important in mature field development to quantify incremental reserves and to minimize the uncertainties in reservoir characterization. Fluid contacts will move throughout the life of the field, and water saturations can be variable and unknown as a result of production and injection operations. In horizontal wells, conventional LWD wave propagation resistivity tools are influenced by bed boundary effects and by the presence of macro-anisotropy in laminated sand-shale sequences, making it very difficult to determine true formation resistivity necessary for petrophysical interpretation. Modern azimuthal deep resistivity tools provide a large number of quantitative azimuthal resistivities that are valuable for formation evaluation in complex horizontal wells, as well as very deep reading geosignals that provide real-time geosteering information. Resistivity modeling is key for pre-job planning and in interpreting complex logs responses after the well is drilled. The case studies in this paper have shown how this technology can assist in the development and evaluation of mature fields. ACKNOWLEDGEMENTS The authors would like to thank the management of the customers who case studies were used in this paper and to Halliburton for their encouragement and permission to publish this work. REFERENCES Bittar, M Electromagnetic wave resistivity tool having a tilted antenna for geosteering within a desired payzone. US Patent 6,476,609, November 5, Bittar, M., Klein, J., Beste, R., Hu, G., Wu, M., Pitcher, J., Golla, C., Althoff, G., Sitka, V., Minosyan, V., and Paulk, P A new azimuthal deep-reading resistivity tool for geosteering and advanced formation evaluation. Paper SPE presented at the SPE Annual Technical Conference and Exhibition, Anaheim, California, USA,11-14 November. Bittar, M., Chemali, R., Morys, M., Wilson, J., Hveding, F., Li, S., Knizhnik, S., and Halverson, D.M The depth-of-electrical image a key parameter in accurate dip computation and geosteering. Paper presented at the SPWLA 49th Annual Logging Symposium, Edinburgh, Scotland, U.K., May. Bittar, M., Chemali, R., Pitcher, J., Cook, R., and Knutson, C Real-time proactive optimal well placement using geosignal and deep images. Paper OTC presented at the Offshore Technology Conference, Houston, Texas, USA, 3-6 May. Clarke, D.D. and Henderson, C., eds., The stratigraphy of the Wilmington oil field, Geologic Field Guide to the Long Beach Area, Pacific Section AAPG Guidebook, p

14 Mayuga, M.N Geology and Development of California's Giant - The Wilmington Oil Field, presented to the American Association of Petroleum Geologists, 53rd Annual Meeting, Oklahoma City, Oklahoma, USA, April. Pitcher, J., Bittar, M., Hoyt, D., and Henderson, J. 2009b. Improving recovery with advanced formation evaluation and well placement techniques in thinly laminated sand-shale reservoirs. Paper presented at the Offshore Mediterranean Conference and Exhibition, Ravenna, Italy, March. Pitcher, J., Bittar, M., Hinz, D., Knutson, C. and Cook, R Interpreting azimuthal propagation resistivity: a paradigm shift. Paper SPE presented at the SPE EUROPEC/EAGE Annual Conference and Exhibition held in Vienna, Austria, May. ABOUT THE AUTHORS Mike Dautel is Eurasia Pacific Regional Petrophysics Manager for Sperry Drilling based in Kuala Lumpur, Malaysia. He is responsible for LWD log interpretation and petrophysical support, the development of geosteering services, and the introduction of new LWD technology. Mike has 26 years of experience in the oilfield and has worked in Australia, USA, Middle East, and Asia. He began as a wireline logging engineer before moving into LWD operations, technical support, tool and software development, and log interpretation. Mike holds an honors degree in electrical engineering and a masters degree in information technology from the Queensland University of Technology; he is a member of SPWLA and SPE. Michael Bittar is a Senior Director of Technology for Middle East and North Africa for Halliburton in Dhahran Saudi Arabia. Michael joined Halliburton in 1990 and has contributed to the advancement of logging-while-drilling and wireline sensor technology and interpretation. Since joining Halliburton, Michael held several technical and leadership roles, including Halliburton Technology Fellow, Director of Research, and Senior Director of Formation Evaluation. Michael received his BS, MS, and PhD degrees in electrical engineering from the University of Houston and has more 100 patents and publications relating to formation evaluation and downhole measurement. Michael is a long-term member of the SPWLA and SPE and the recipient of 2006 SPWLA Technical Achievement Award. Jason Pitcher is the Global Well Placement Solutions Champion for Halliburton - Sperry Drilling based in Houston, Texas. He received his BS degree in geology from the University of Derby and his MS degree in mineral exploration from Imperial College in London. Jason has more than 20 years of experience with Sperry Drilling, having worked in multiple areas of data acquisition and interpretation. He has developed and managed well placement operations around the world, contributing to multiple national and international geosteering campaigns. He has co-authored more than 15 papers and articles on LWD tools, petrophysics, geosteering, and geosteering tools. He currently sits on the technical paper review committee of the SPWLA and is an active educator in geosteering. 14