3HW6FL   477 DOI 10.1007/s12182-013-0298-x

Study of real-time LWD data visual interpretation and geo-steering technology

Shao Cairui1 , Zhang Fuming1, Chen Guoxing1, Ji Jiaqi2, Hou Qinggong3, Tang Jianhong2 and Cao Xianjun1

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© China University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg 2013

Abstract:/:' ORJJLQJZKLOHGULOOLQJ GDWDKDVEHHQXVHGWRH[SORUHFRPSOH[VXEWOHUHVHUYRLUVE\UHDO time visual interpretation and geo-steering. The method comprises of computer communication, well log data processing, formation recognition, reservoir modeling and model updating in real time. We studied WKHNH\WHFKQRORJLHVUHODWHGWRUHDOWLPH/:'GDWDYLVXDOLQWHUSUHWDWLRQDQGJHRVWHHULQJDQGGHYHORSHG computer software with Chinese intellectual property rights covering the following important aspects:  UHDOWLPHFRPSXWHUFRPPXQLFDWLRQRIZHOOVLWH/:'GDWD YLVXDOL]DWLRQRIJHRORJLFDOPRGHODQG ERUHKROHLQIRUPDWLRQ UHDOWLPHLQWHUSUHWDWLRQRI/:'GDWD UHDOWLPHJHRORJLFDOPRGHOXSGDWLQJ DQGJHRVWHHULQJWHFKQRORJ\:HXVH¿HOGDSSOLFDWLRQH[DPSOHVWRGHPRQVWUDWHWKHIHDVLELOLW\DQGYDOLGLW\ of the proposed technologies.

Key words: /:' ORJJLQJZKLOHGULOOLQJ UHDOWLPHYLVXDOL]DWLRQLQWHUSUHWDWLRQJHRVWHHULQJ

1 Introduction software related to the tool hardware, together with drilling engineering control software, making their service more /:' ORJJLQJZKLOHGULOOLQJ WHFKQRORJLHVKDYHEHHQ competitive (Shao et al, 2010). undergoing rapid development along with the wide use of The high service price and technological monopoly of high-angle well directional drilling technology to develop WKRVHLQWHUQDWLRQDOFRPSDQLHVOLPLWWKHZLGHXVHRI/:' WKLQDQGVXEWOHRLODQGJDVUHVHUYRLUV/:'LVXVHGQRWRQO\ technology, especially in low-budget situations. Therefore in formation evaluation when wireline logging is unavailable, UHVHDUFKLQWRUHDOWLPH/:'GDWDYLVXDOLQWHUSUHWDWLRQDQG but also for geo-steering into complex reservoirs to control geo-steering technology with Chinese intellectual property the down-hole drill tool to hit the desired geological targets rights is of great importance. For this purpose, the authors 6DLNLD6ZLUHHWDO/LXHWDO  studied the key technology and developed corresponding /:'WHFKQRORJ\KDVPDGHJUHDWSURJUHVVLQWKHODVW software. Field application examples were used to GHFDGH/:'QXFOHDU 0LFNDHOHWDO:KHHOHUHW demonstrate the feasibility and validity of the proposed DO DQGHOHFWULFDO 5RVWKDOHWDO%D]DUDHWDO software. 2013) tools can now obtain measurement results that are comparable to those of wireline logging tools. Besides, the 2 Real-time reception of LWD data at well /:'UHVSRQVHEHLQJPHDVXUHGZKLOHGULOOLQJLVFORVHUWRWKH site true formation value than the later wireline logging obtained after drilling. Great success has also been achieved in sonic 5HDOWLPHUHFHSWLRQRI/:'GDWDLQWKHILHOGVHWVWKH /:'WHFKQRORJLHV 7DQJHWDO DQG105 +HDWRQ foundation for the implementation of real-time interpretation et al, 2012). Schlumberger, Halliburton and Baker Hughes and geo-steering. KDYHPDGHUHPDUNDEOHDFKLHYHPHQWVLQWKH/:'¿HOG7KH Vision and Scope (www.slb.com/services/drilling/mwd_ 2.1 Standard format of WITS OZGDVS[ VHULHVRI6FKOXPEHUJHU/:'WRROVDUHH[DPSOHV ,QJHQHUDOGRPHVWLFDQGLQWHUQDWLRQDO/:'JURXQG RI/:'WHFKQRORJ\HYROXWLRQ)RUWKHLU/:'VHUYLFHWKHVH control systems can provide a real-time data port for sending companies also provide reservoir evaluation and geo-steering data to a third party, with a logical data recording structure. The international WITS (Well Information Transform *Corresponding author. email: [email protected] Standard) format structure is widely utilized. The WITS format is consistent with the POSC (Petro-technical Open 5HFHLYHG-XQH 478 3HW6FL  

6RIWZDUH&RUSRUDWLRQ VWDQGDUG7KHUHDUHVWDQGDUGUHFRUG NLWVFDQEHXVHG7KHRSHQJUDSKLFVOLEUDU\2SHQ*/ ZZZ definitions (home.sprynet.com/~carob/) for all the drilling RSHQJORUJ/LHWDO SURYLGHVDSRUWDEOHVWDQGDUGDQG and measurement information at the well site. The 07 record open function package supporting different operating systems is used for hole trajectory data (depth measurement, well and GUIs (Graphical User Interfaces), which is an economic GHYLDWLRQDQGD]LPXWK DQGWKHUHFRUGLVIRUWKH/:' and simple 3D visualization SDK (Software Development data. WITS has both text and binary code formats. The record Kit). In MS Windows, Visual C++ is the first choice as the of text code starts with the punctuation mark “&&” and ends *8,GHYHORSPHQWWRROIRU2SHQ*/JUDSKLFDSSOLFDWLRQV by the punctuation mark “!!”. Each line between “&&” and “!!” contains one data item. Each data item includes three 3 Geometry steering based on a pilot SDUWVGDWDUHFRUGLGHQWL¿FDWLRQGDWDLWHPLGHQWL¿FDWLRQDQG geological model and wellbore information data item value (Table 1). visualization Table 1 WITS data record example 3.1 3D visualization of pilot geological model Data record Record Data item Data item Illustration Pilot geological models can be obtained by formation line mark mark value correlation or geological modeling. Using Microsoft (www. && Start of record PLFURVRIWFRP 9& :DQJHWDO DQG2SHQ*/ZH  08  090802 Date is August 2, 2009 have developed software that can display a geological model

0806090336 08 06 090336 Time is 9:3:36 a.m. LQ'7KHUHIRUHWKHJHRORJLFDOVWUXFWXUHFRQ¿JXUDWLRQDQG formation boundaries can be effectively visualized from Measure depth of borehole 08087849.820 08 08 7849.82 different angles of view. is 7849.82 True vertical depth For a 3D regular grid model, the node vertex is arranged  08 09  RIERUHKROHLV in accordance with the horizontal and vertical directions. In Measure depth of bit a general way, lots of small cubes are drawn for the eight  08 10  LV adjacent nodes. Then, many such cubes form a large scale True vertical depth of bit  08 11  geological structure. This method has high time and space LV FRPSOH[LW\IRUODUJHJHRORJLFDOPRGHOV /RUHQVHQDQG&OLQH Measure depth of gamma  08 21  1987). To reduce the complexity, we adopt a hollow display LV method which only displays the six external surfaces of the True vertical depth  08 22  RIJDPPDLV JHRORJLFDOPRGHODV)LJ /HYR\%DULOORW )RU displaying and analyzing the inner structure section slices are 082479.000 08 24 79 The value of gamma is 79 cut in different directions (Fig. 2). If the geological model !! End of record is complex, we use irregular grid data to store and display it (Pears et al, 2012). 2.2 Real-time reception of WITS data with Socket network communication technology The interface of the Socket is an application programming interface (API) of a TCP/IP network. Programmers can use it to develop applications on TCP/IP network. The interface of WKH6RFNHWZDV¿UVWO\UHDOL]HGLQWKH81,;RSHUDWLQJV\VWHP and then transported to other operating systems including 06:LQGRZV -RQHVDQG2KOXQG 7KHSRLQWWRSRLQW Winsock technology can complete the peer-to-peer computer data communications for wellsite upload. The wellsite WITS data generally uses the datagram socket transmission. Fig. 1 Hollow display of geological model Using the above technology, the real-time borehole trajectory and logging data for each measurement depth can be obtained through receiving and decoding WITS data. The following is an example for the real-time GR logging data.

#WITS Curve GR Attribute Items: # Dep Tvd HoleDep HoleTvd BitDep BitTvd Value Incl Azim  -2024.4 ...... In order to implement geo-steering, the geological -5677.5 background model and wellbore data must be displayed in 3D in order to visualize the wellbore trajectory in the geological background. Many 3D visualization software development Fig. 2 Slices in different directions 3HW6FL   479

3.2 Visualization of well trajectory & borehole data interpolation with its measured depth and the 3D trajectory information data. The minimum radius of curvature trajectory calculation 2) Use the method of least squares to get the well PHWKRG 6DZDU\QDQG7KRURJRRG LVXWLOL]HGWR trajectory plane equation, and then get the maximum inclined calculate the three-dimensional coordinates of the drilling section plane of the trajectory. trajectory from the real-time measurement-while-drilling 3) Use the plane equation and 3D coordinates of each (MWD) data (depth, well deviation and deviation azimuth). logging point, calculate the 3D coordinates with amplitude 7KHQWKHGUDZOLQHIXQFWLRQRIWKH2SHQ*/$3,LVXVHGWR variation of each scaled log data value. sequentially connect the 3D coordinate trajectory control 4) Connect each log data point according to their 3D points in 3D space. This way, a 3D borehole trajectory is coordinates, display the 3D well logging curve. displayed as Fig. 3. Note that the 3D log curve attributes (such as scale, color, 3D visualization of a log curve is done by actually width) can be adjusted to enhance the visual effect. displaying the amplitude of 3D points V(x, y, z) in 3D space, The scattered core data, segmented wellbore information so it can be regarded as 4D data visualization. The drawing such as log interpretation results (layer porosity, permeability, methods are as follows: DQGÀXLGVDWXUDWLRQ FDQDOVREHGLVSOD\HGDV'ORJFXUYHV 1) Get 3D coordinates of each logging point by or 3D column (see right of Fig. 3).

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Fig. 3 Visualization of well trajectory and log data (different colors of column on right represent different rock types) 3.3 Visual steering based on a pilot geological model Contrast the difference between the designed trajectory & wellbore information and the drilled trajectory by the 3D well trajectory visualization. 3.3.1 Geometry steering using wellbore trajectory and Display the contact relationships between trajectory and geological model in 3D formation by cutting the geological model and displaying the 7KURXJKWKHVSHFL¿HGYLVXDOL]DWLRQPHWKRGRISRLQWOLQH ZHOOSUR¿OHDORQJWKHZHOOWUDMHFWRU\ )LJDQG)LJ  surface, body and trajectory in 3D space, we implemented 8VLQJURWDWLRQ]RRPDQGSDQWRYLHZWKHVSHFL¿HGWDUJHW WKHYLVXDOL]DWLRQRIWKHSLORWJHRORJLFDOPRGHOZHOOSUR¿OHV and to walk through the wellbore trajectory in the geological of stratigraphic correlation, well trajectory, and wellbore data body from any angle. (core mark, log data and reservoir parameters) in a composite Through analysis of contact relationship among designed view background. Thereby we can visually describe the trajectory, drilling trajectory, and pilot geological model using contact relationship of the well trajectory and geological body the above functions, we can implement geometric steering using the following functions: effectively. -120.00

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Fig. 4 Well trajectory display based on a stratigraphic correlation model (different color lines are different well trajectories, and the symbols on the top are the ground well sites) 480 3HW6FL  

trajectory and pilot geological model (Fig. 6). This way, we can view the borehole trajectory horizontal deviation in the top projection display and the contact relationship between borehole trajectory and formation in the pilot strata model in DVSHFL¿HGGLUHFWLRQVRDVWRSURYLGH'JHRPHWULFFULWHULD for controlling the well trajectory. 4 Real-time interpretation and geo-steering using LWD data 2QO\ZLWKUHDOWLPHLQWHUSUHWDWLRQRIWKH/:'GDWD can the borehole trajectory and the reservoir information FRQWDLQHGLQWKH/:'GDWDEHGLVSOD\HGLQUHDOWLPH$QG Fig. 5 Geological body cutting along the well trajectory only by this, can the formation interface, the lithology YDULDWLRQDQGWKHÀXLGLQIRUPDWLRQEHLQWHUSUHWHGLQWLPH$OVR 3.3.2 Auxiliary steering with 2D projection relationship only by this, can we update geological model in real time, and To view different trajectories (such as designed trajectory adjust the drilling trajectory into the oil or gas layers. This DQGGULOOLQJWUDMHFWRU\ DQGJHRORJLFDOLQWHUIDFHVLQDVSHFL¿HG ZD\DQLQWHJUDWHGWHFKQRORJ\IRU/:'LQWHUSUHWDWLRQDQG view angle, we provide top and side projection display of well geo-steering can be realized.

800 700

700 Well head Real well trajectory 750 Designed well trajectory 600 800

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North offset, m 950 200 True vertical depth, m Real well trajectory 1000 100 Designed well trajectory

0 1050 0 20 40 60 80 100 120 140 160 180 0 100 200 300 400 500 600 700 800 900 East offset, m Horizontal offset, m (Max offset azimuth: 12 degrees)

Fig. 6'SURMHFWLRQGLVSOD\RIZHOOWUDMHFWRU\ /HIWWRSYLHZULJKWVLGHYLHZ 4.1 Visual real-time interpretation with LWD data 1) Shale content This parameter is estimated from the GR curves using the 4.1.1 Pretreatment of LWD data conventional formula: 7KH/:'GDWDJHQHUDOO\KDYHORZPXGLQYDVLRQEXW are strongly influenced by the well deviation angle and GCURu SH GR GR 21i  VXUURXQGLQJOD\HUV /LXHWDO 7KHUHIRUHEHIRUH SH min , V (1) GR GR sh 21GCUR quantitatively calculating reservoir parameters, corrections max min for well inclination and the surrounding rocks should be where GRLVORJGDWDGR is the log data of pure shale made. max IRUPDWLRQGR LVWKHORJGDWDRIDSXUHVDQGIRUPDWLRQ 4.1.2 Reservoir parameters interpretation models min GCURLVWKHUHJLRQH[SHULHQFHFRHI¿FLHQWZKLFKHTXDOV The reservoir parameters can be estimated using pre- in the Tertiary formation and 2.0 in the old formation. GCUR SURFHVVHG/:'GDWD*XLGHGE\WKHZLUHOLQHORJJLQJ can be obtained from local data. interpretation method, the shale content, parameters such 2) Porosity estimation with statistical shale content model as porosity, oil or water saturation, and permeability, can be If there is no porosity log data (acoustic, density and estimated with the shale sands equivalent volume model. neutron log), the porosity can be estimated by the relationship Appropriate models for the estimation can be used (Yong between shale content and porosity. The statistics of DQG=KDQJ6FKOXPEHUJHU:LUHOLQH 7HVWLQJ  experimental data show that there is a relationship between )RUWKHSUHVHQWGRPHVWLFPDUNHWPRVW/:'PHDVXUHPHQWV shale content and porosity. For example a regression model only provide gamma-ray (GR) and resistivity log data. Only can be found below. a few individual companies supply the compensated neuron 2 ORJ &1/ DQGGHQVLW\ORJGDWD7KHUHIRUHWKHUHVHUYRLU PORii Au(1)(1) SH u B SH i  C (2) parameters are estimated using statistical models as follows: th where PORi is the porosity value at i SRLQWSHi is the relative 3HW6FL   481

1 DPRXQWRIVKDOHA, B and CDUHWKHUHJUHVVLRQFRHI¿FLHQWV n §·abR˜˜ 3) The matrix volume w Sw ¨¸m  With the estimation of the shale content and porosity, the ©¹I ˜ Rt matrix volume can be estimated by the volumetric model: where a is the lithological index, m is the pore structure index, n is the saturation index. VPORVma 1  sh (3) &XUUHQWO\WKH/:'ORJVXVXDOO\RQO\KDYHJDPPDDQG resistivity data. Therefore, we can only evaluate the shale 4) Permeability quantitatively. The porosity and saturation parameters can When the rock physical property experimental data are only be estimated using a statistical model referencing to the available, the permeability can be calculated by the regression wireline log evaluation results of nearby wells. equation of porosity, shale content and permeability or 4.1.3 Real-time visual interpretation of LWD data WKURXJKWKH7LPXUHPSLULFDOIRUPXOD 7LPXU%DODQHW Because the reservoir property interpretation model and al, 1997). SDUDPHWHUVDUHGLIIHUHQWIRUGLIIHUHQWUHJLRQV¿HOGHQJLQHHUV 5) Formation water saturation in different regions need to use different interpretation (1) In shale sandstone formation, the Simandoux formula models. For this requirement, we designed and developed 6LPDQGRX[)HUWODQG+DPPDFN3HHWHUV  a generic reservoir property interpretation model, called a can be utilized to estimate the water saturation. model generator, which can generate an appropriate local interpretation model by inputting and adjusting the model formula and parameters. 1 ­½0.81RR °°ww (4) The interpretation model and specific parameters can SVwsh ®¾ I ¯¿°°RRtsh0.4 be input using the reservoir property interpretation model generator, so that we can calculate the reservoir parameters where Rw is formation water resistivity, Rt is formation LQUHDOWLPHXVLQJWKHUHDOWLPH/:'GDWDDQGWKHQGLVSOD\ resistivity, and Rsh is mud resistivity. the interpretation results using the real-time display software (2) In clean sandstone formation, the Archie formula module (Fig. 7). (Archie, 1942) can be utilized.

D 150 200 250 300 350 400 450 500 550 150.00 GR GR 0.0C Rt 1000.00 1000.00 DR SR 1.C 1.C 0.00 1.00 VSH VSH H: 1:1900 POR VSH SAND Result SHALE 0.00 1.00 POR 0.00

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4.2 Real-time updating of geological models and geo- 4.2.1 Real-time updating method of formation structure steering The formation structure parameters include thickness, dip angle, azimuth, etc. Because of the uncertainty of the pilot geological model, 1) Using the spatial relationship between the geological the target of the designed well path is often inconsistent with model and wellbore information the actual strata. Therefore, in order to realize geo-steering With the help of 3D visualization and 2D projection HIIHFWLYHO\WKHFRQ¿JXUDWLRQRIVWUDWDDQGUHVHUYRLUSURSHUWLHV decomposition techniques, we can observe and analyze the need to be updated in real time based on the interpretation of formation properties from different perspectives along the /:'GDWD7KHQWKHSURSRVHGZHOOWUDMHFWRU\FDQEHDGMXVWHG well trajectory, project the drilling path into the formation, as a result of the updated information. GHWHUPLQHWKHDFWXDOIRUPDWLRQERXQGDULHVXVLQJ/:'FXUYHV 482 Pet.Sci.(2013)10:477-485 and update the strata model properly. We get the dip angle as: 2) Using the intersections of the well trajectory and formation boundaries to estimate the formation thickness D tan1 (De /' D ) I 90 (7) and dip angle During the drilling of highly deviated and/or horizontal Using Eq. (7), we can provide a real-time estimation of the wells, S-shaped drilling paths tend to occur repeatedly dip angle for the formation being drilled through. in target strata because of the uncertainty of the initial strata model, an excessive decrease or increase of drill bit inclination, and the lack of near-bit information due to LWD position lagging the drill bit (Fig. 8) as the drill is further down the hole than the LWD sensors. Well trajectory

Well trajectory Inclined formation A I ș h 2

h 1 C I h ƍ ș1 90° 90– Į 1 H B ȕ The initial strata model h 3 De ǻD

Fig. 8 Estimating formation thickness variation using well trajectory and LWD curves Fig. 9 Diagram illustrating the dip angle determination using the azimuthal LWD data

The real-time interpretation of LWD data can help If the azimuthal LWD measurements are penetrating determine the contact positions of the well trajectory and enough, such as deep azimuthal resistivity measurements formation boundaries (points A, B, C), which enable us to (PeriScope of Schlumberger and ADR of Halliburton), the calculate formation thickness according to the well trajectory position of the formation boundary and dip angle can be FRQ¿JXUDWLRQZLWKLQWKHIRUPDWLRQERXQGDULHVGHWHUPLQHWKH estimated in real-time before the measurement point touches the boundary. variation of formation thickness and dip angle, and reduce 4.2.2 The method for real-time updating reservoir the uncertainty of the formation structure model for drilling property parameters steering. In order to update the reservoir property parameters, it Through the two-dimensional projection displayed in is necessary to determine the formation lithology, physical horizontal and vertical planes (Fig. 6), we can visually properties, and fluid type in real time. Since the gamma- determine the relation between the well trajectory and the ray and resistivity log data are usually available from LWD formation boundaries. Then, by using the above method we measurements, the following methods can be utilized to can quickly estimate the thickness variation of the formation estimate these reservoir properties. model. 1) Lithology determination 3) Determining the formation dip angle using the The lithology variation of the drilled formation can azimuthal LWD data be determined by the LWD gamma-ray data, according to Using the LWD azimuthal data, we can determine the features of gamma-ray curve in the sand-shale formation. intersection positions of the high side and low side of the In addition, the lithology variation can also be determined borehole relative to formation boundaries and calculate the by the stratigraphic correlation of log curve characteristics of depth difference between the top and bottom intersection the marker beds in nearby wells. According to the 2D or 3D positions along the borehole axis. Combining this with the visualization of the stratigraphic correlation, and the log curve well deviation angle and borehole diameter, we can calculate characteristics of LWD and the marker beds, we not only can the formation dip angle (Efnik et al, 1999). Fig. 9 shows the estimate the lithology of the current formation being drilled, principle of determining dip angle using the azimuthal LWD but also can judge whether the target layer has been reached. data. Suppose that the well deviation angle is I, formation dip Fig. 10 displays the contrast diagram of one work area. The angle is ĮǻD is the depth difference between the top and characteristics of the real-time LWD data (Well B) are similar bottom intersections of the formation and the borehole, De is to those of the adjacent well near the top of the reservoir the borehole diameter. LQWHUYDOZKLFKVLJQL¿HVWKDWWKHWDUJHWOD\HUKDVEHHQUHDFKHG Using the geometric relationship: 2) Determination of reservoir physical properties and ÀXLGW\SH (6) According to the above LWD data interpretation method, 3HW6FL   483

Well A Well B Well C

Gamma ray Resistivity Gamma ray Resistivity Gamma ray Resistivity RT RT RT 120 ȍ.m) 120 ȍ.m) 120 ȍ.m) DEP DEP DEP GR RI GR RI GR RI 0(API) 150 120 ȍ.m) 0(API) 150 120 ȍ.m) 0(API) 150 120 ȍ.m) 1500 1510 1500 1500 1510 1510 1520 1520 1520

Fig. 10 Using stratigraphic correlation to determine the target layer we can estimate the shale volume, porosity, saturation, %DVHGRQWKHUHDOWLPHLQWHUSUHWDWLRQRI/:'GDWDDQG and permeability quantitatively in real time, yielding the geological model updating, together with the 3D visualization formation parameters along the well trajectory. Then using of the wellbore geological information and geological model, these parameters as hard constraints and utilizing a proper we can visually analyze the difference between the actual modeling method, we can update the properties of the formation model and the prior model. The procedure allows geological model quickly at the well site. us to adjust the well path in a timely manner and ultimately 4.2.3 Real-time updating of the geological model and geo- realize drilling geo-steering in 3D space. steering 4.2.4 Example During the drilling process, we can update the geological Fig. 12 displays the geo-steering example of a well in PRGHOLQUHDOWLPHXVLQJWKH/:'GDWDSURFHVVLQJDQG western China. The solid red line on the GR track in the top interpretation results and the structure and property window is the forward modeled gamma-ray response curve, determination method mentioned above. The geological and the blue one is the measured gamma-ray curve. The lower PRGHOXSGDWLQJÀRZFKDUWLVLOOXVWUDWHGLQ)LJ right side window shows the actual formation model (the

Log response forward Building pilot The true logging simulation using the geologic model response and well path updated geologic model and adjusted well path

Real time interpretation of Adjust well path LWD data Forward modeling log response Comparison of Update measured and geologic model modeled response Pre-drilling work Drilling process

Fig. 117KHUHDOWLPHÀRZFKDUWIRUJHRORJLFDOPRGHOXSGDWLQJEDVHGRQWKH/:'GDWDLQWHUSUHWDWLRQ 484 3HW6FL   yellow-shaded background is sandstone, and the gray-shading measured gamma-ray response results, we can judge that is mudstone) and the borehole trajectories (the blue one is the the well trajectory has touched the bottom boundary of the designed trajectory, and the red one is the drilled trajectory). reservoir. The drilling is then adjusted by gradually increasing It can be seen from the figure that the target landing point the well deviation angle to re-enter the target layer. is at 1,624 m depth. From then on, the drilled wellbore 8VLQJWKHDERYHPHWKRGIRUUHDOWLPH/:'GDWD trajectory is kept steadily in the target layer by building interpretation and geological model updating, we estimate and holding the inclination angle of the drill bit. Real-time that the thinnest reservoir stratum confining the well interpretation results of the reservoir parameters show that WUDMHFWRU\LVDERXWP0RUHRYHUZLWKUHDOWLPH/:'GDWD the gamma-ray log value (shale content) increases over the interpretation and geological model updating, the well path horizontal distance 284-304 m. Combining modeled and can be accurately adjusted. The procedure results in a landing measured gamma-ray response curves we can judge that the depth at 1,624 m, which is 36 m ahead of the designed depth. top boundary has been encountered. Afterwards, the drilling The vertical depth of the oil formation top is 2.4 m higher is steered to reduce the well deviation angle to drill back into than the originally estimated depth. The borehole horizontal WKHUHVHUYRLU5HDOWLPH/:'LQWHUSUHWDWLRQUHVXOWVVKRZWKDW OHQJWKLQIRUPDWLRQLVPORQJHUWKDQWKHSUHGHVLJQHG the shale content increases again in the horizontal distance OHQJWK7KH¿QDOZHOOWUDMHFWRU\KDVDVXFFHVVUDWHRI LQWHUYDOP$JDLQE\FRPSDULQJWKHPRGHOHGDQG within the oil formation.

D 160 180 200 220 240 260 280 300 320 340 360 380 400 420 Date: - 120.00 120.00 GR GR MGRR 60.00 Vert: 1:200 20.00 60.00 100.00 100.00 Well B Rt R40 R05 R20 R10 0.00 2.00 20.00 2.00 0.00 YSH

YSH 100.00 P0R

YSH Shale Sand Horz: 1:1000

FOR Lithology 0.00 1.00 0.00 1.00 1510

Top boundary TVD: 1516.5m 1515 1619.33 1705.70 1753.49 1861.00 1657.64 1801.59

Land point: 1624m 1520

Fig. 12 An application example for a well in western China (D: displacement)

5 Conclusion 0DMRU3URMHFWVRI2LO *DV =; DQG³´ 3URMHFWV $$ ,QDGGLWLRQZHWKDQN3URIHVVRU 8VLQJUHDOWLPHLQWHUSUHWDWLRQRI/:'GDWDDQGJHRORJLFDO Tang Xiaoming for the thoroughgoing revision of the paper. model and borehole information visualization, combining with the integrated application of computer communications References and 3D visualization technology, we developed a software application for three-dimensional visualization drilling Archie G E. The electrical resistivity log as an aid in determining some reservoir characteristics. Transactions of the AIME. 1942. 146(1): geo-steering, providing a useful geo-steering technology  with Chinese intellectual property rights. The software has Bal an B, Mohaghegh S and Ameri S. State-of-the-art in permeability been applied in a number of domestic oil fields, with good determination from well log data: Part 1—A comparative study, results, enabling domestic drilling industries to become more model development. SPE Formation Evaluation. 1997. 12(3): 170- competitive and enabling oil companies to reduce cost in 174 (SPE 30978) drilling their wells. Some shortcomings and problems are Bar illot C. Surface and volume rendering techniques to display 3-D data. also found in the application, which need further research and IEEE Engineering in Medicine and Biology Magazine. 1993. 12(1): development. 111-119 %D]DUD00DDORXI-$O6KDUDIL0HWDO/RJJLQJZKLOHGULOOLQJ Acknowledgements resistivity images for geosteering. 18th Middle East Oil & Gas Show and Conference (MEOS), 10-13 Mar 2013. Bahrain International The research work is funded by several Co. of CNPC Exhibition Centre, Manama, Bahrain (SPE 164220-MS) and SINOPEC, and China National Science and Technology (IQLN06+DPDZL0$O6KDPUL$HWDO8VLQJQHZDGYDQFHVLQ/:' 3HW6FL   

technology for geosteering and geologic modeling. Middle East Saikia K. Real-time modeling-while-drilling for optimized geosteering Drilling Technology Conference, 8-10 November 1999. Abu Dhabi, and enhanced horizontal well placement in thin and complex 8QLWHG$UDE(PLUDWHV 63(,$'&  reservoirs. 6th International Petroleum Technology Conference, 26- Fer tl W H and Hammack G W. A comparative look at water saturation 0DU%HLMLQJ&KLQD ,37& FRPSXWDWLRQVLQVKDO\SD\VDQGV7KH/RJ$QDO\VW   6DZDU\Q6-DQG7KRURJRRG-/$FRPSHQGLXPRIGLUHFWLRQDO 20 calculations based on the minimum curvature method. SPE Drilling +HDWRQ1-DLQ9%ROLQJ%HWDO1HZJHQHUDWLRQPDJQHWLFUHVRQDQFH &RPSOHWLRQ   63(3$ while drilling. SPE Annual Technical Conference and Exhibition, 6FKOXPEHUJHU:LUHOLQH 7HVWLQJ/RJ,QWHUSUHWDWLRQ3ULQFLSOHV 8-10 October 2012. San Antonio, Texas, USA (SPE 160022-MS) $SSOLFDWLRQV6XJDU/DQG7H[DV0DUFK -RQHV$DQG2KOXQG-1HWZRUN3URJUDPPLQJIRU0LFURVRIW:LQGRZV 6KDR&57DQJ+4DQG=KDQJ)0&XUUHQWVLWXDWLRQDQGUHVHDUFK Washington: Microsoft Press. 2002 WUHQGRIWKHHYDOXDWLRQWHFKQLTXHIRU/:'LQWHUSUHWDWLRQ3HWUROHXP /HYR\0'LVSOD\RIVXUIDFHVIURPYROXPHGDWD,(((&RPSXWHU *HRORJ\ 2LO¿HOG'HYHORSPHQWLQ'DTLQJ   LQ Graphics and Applications. 1988. 8(3): 29-37 Chinese) /LX6/XFDV-/3OHPRQV3$HWDO&KDOOHQJHVWRJHRVWHHULQJDQG Simandoux P. Dielectric measurements in porous media and application completion optimization of horizontal wells in the Cotton Valley WRVKDO\IRUPDWLRQV5HYXHGH/¶,QVWLWXW)UDQoDLVGX3pWUROH Formation, East Texas. 2013 SPE Middle East Unconventional Gas 6XSSO,VVXH &RQIHUHQFH ([KLELWLRQ-DQ0XVFDW6XOWDQDWHRI 6ZLUH3%DGU<5DPDGDQ=-HWDO6WHHULQJZLWKWKHPXOWLIXQFWLRQ Oman (SPE 163979-MS) /:'WRRODFKLHYHVRSWLPXPUHVXOWVLQKLJKVWUXFWXUDOXQFHUWDLQW\ /L<;XH+%=KX%/HWDO2SHQ*/)XQFWLRQZLWK([DPSOH3DUVH ¿HOGLQ(J\SWWK0LGGOH(DVW2LO *DV6KRZDQG&RQIHUHQFH Manual. Beijing: National Defence Industry Press. 2002. 1 (in (MEOS), 10-13 Mar 2013. Bahrain International Exhibition Centre, Chinese) Manama, Bahrain (SPE 164282-MS) /RUHQVHQ:(DQG&OLQH+(0DUFKLQJFXEHV$KLJKUHVROXWLRQ' 7DQJ;03DWWHUVRQ'DQG:X/0HDVXUHPHQWRIIRUPDWLRQ surface construction algorithm. ACM Siggraph Computer Graphics. SHUPHDELOLW\XVLQJ6WRQHOH\ZDYHVIURPDQ/:'DFRXVWLFWRRO 1987. 21(4): 163-169 3HWURSK\VLFV   0LFNDHO03KHOSV'DQG-RQHV''HVLJQFDOLEUDWLRQFKDUDFWHUL]DWLRQ Timur A. An investigation of permeability, porosity, and residual water and field experience of new high-temperature, azimuthal, and VDWXUDWLRQUHODWLRQVKLSIRUVDQGVWRQHUHVHUYRLUV7KH/RJ$QDO\VW spectral gamma ray logging-while-drilling tools. SPE Annual 1968. 9(4): 8 Technical Conference and Exhibition, 29 September - 2 October, :DQJ+