FMI Borehole geology, geomechanics and 3D reservoir modeling
Applications s
Structural ge geolo olog gy q
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Structural dip, even in fractured and conglomeratic formations
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Sedimentary dip
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Paleocurrent Paleocurre nt direction di rection
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Sedimentary bodies and their boundaries Anisotropy, permeability barriers and paths
Thin Th in--bedded re res serv rvoir oirs s
q
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Rock textu texture re q
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Carbonate texture
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Secondary Second ary porosity porosi ty
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Fracture systems
Complement to whole Complement whole core, cor e, sidewall core and formation tester programs
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q
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80%borehole coverage in 8-in. hole size
s
0.2-in. [5-mm] image resolution in vertical and azimuthal directions
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fully processed images and dip data in real time
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top combinable with other wireline tools such as the ARI* Azimuthal Resistivity Im I mager and and AIT* AI T* Array Array Induction Imager Tool.
Depth matching and orientation tat ion for f or whole whol e cores cores Reservoir description of intervals not cored Depth matching for sidewall core samples and MDT* Modular Formation Dynamics Tester probe settings
The The FMI tool generat rates an elec lectric rical image of the borehole from 192 microresistivity measurements. Special focusing circui circuitry try ensures that the measuri asuring ng currents are forced into the formation, where they are modulated in amplitude with the formation conductivities to produce both low-fr l ow-freq equen uency cy sign signals als rich rich with petrophy petrophysical sical and lithological lithological information and a high-resolution component that provides the microresistivity resistivity data used for imag imaging and and dip interpretation. The depth of investigation is about 30 30 in., simil similar ar to that that of shallow lateral resistivity devices. The The ima image is norm ormalize lized thro throu ugh calibration with low-frequency, deeper resistivity measurements from the tool signal or from another resistivity measurement tool.
Geomechanical analysis q
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Qualitative vertical grainsize profile
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The The FMI* Fullbor Fullbore e Formation tion MicroImager provides microresistivity formation images in water-base mud:
Faults
Sedimentary features
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Overview
Drilling-induced features Calibration for f or Mecha Mechanical nical Earth Modeling Mud weight selection
Geology and geophysics workflow q
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Deterministic reservoir modeling Distribution guidance for stochastic modeling Realistic petrophysical parameters
Real-time FMI answers help in making quick exploration, production and drilling decisions.
The The spacin cing of the the button tton elec lectrod trode es, innovative pad and flap design, and high frequency of data transmitted by the digital telemetry telemetry system system result result in a vertical vertical and and azimutha azimuthall resolution of 0.2 in. This means that the dimensions of any feature that is 0.2 in. or larger can be readily estimated from the image. The size of features smaller than 0.2 in. can be estimated by quantifying the current flow to the electrode. Fine-scale details such as 50-micron fractures filled with conductive fluids are visible on FMI logs. The The physics ics of the the FMI measurem rement makes it a highly versatile geological and reservoir characterization tool that produces complete complete and reliable reli able answer answer products. products. Thes These e real-tim real-time answers are used to characterize the rock tectonics, identify and evaluate sedimentary features, measure the rock texture and complement the information obtained from coring programs. FMI data are also used in geomechanical reservoir analysis to identify drilling-induced features such as breakouts. Stress field analysis of FMI data provides critical information for controlling wellbore stability problems through improved design of the mud program.
FMI pad and flap assembly with horizontally offset rows of electrode buttons.
Benefits s
Cost and time savings: complete interpretation with one image pass
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Data obta obtained ined in diffi dif ficult cult environments, including deviated and horizontal wells
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Accurate and reliable interpretation of formation features
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Improve proved d reservoir reservoir des descri cription ption
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Accurate pay estimate
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Well ellsite site answer products for on-site decision making
Features s
Borehole coverage of 80%in 8-in. borehole bor ehole
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High-resolution measurement (nominal 0.2 in.)
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Image details to 50 microns
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Pad tilting for application in deviated and horizontal wells
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High-q High -quality, uality, real-time wellwell site image and Mean Square Dip (MSD) ( MSD) com computa putation tion
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Multiple Multipl e log logging modes: modes: fullbore image, four pad and dipme dipmeter ter
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Top co Top com mbin ina able wit with h mos ostt services
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Excellent signal Excellent signal quali quality ty from focused electric currents
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Electri lectrical cal im i mag ages es less aff affecte ected d by borehole rugosity and washouts
Measurement physics The The figu figure to the the righ right illus illustra trates tes the the FMI measurement principle. An applied voltage causes an alternating current (AC) to flow from each electrode button in the lower pad section through the formation formation to the electrode electrode on the upper cartridge housing. As the current emerges from a button on the pad or flap, its path is initially focused on a small volume of the formation mation directly directly facing the button button.. The The current path expands rapidly to cover a large volume of formation between the lower lower and and upper upper electrodes. electrodes. The current current consists of two components: components: s
high-resolution component, modulated by the resistivity variations in the formation directly facing the button
s
low-resolution component, modulated by the resistivity of the zone between the lower and upper electrodes.
Making the measurement in AC minimizes the effects of what are essentially direct currents created by the friction
of the pads against the borehole wall and by variation of the spontaneous potential (SP). The The micror icrore esistiv istivity ity ima image of the the borehole wall is created from the current measured by the array of buttons. The The high-resoluti high-resolution on component component dominates the image because its value varies from button to button. The lowresolution resoluti on com component ponent appea appears rs only only as a gradually changing background. Microresisti Microresistivity vity changes related related to lithological and petrophysical variations in the rock, which are conveyed mainly by the high-resolution current component, are interpreted on the image in terms terms of rock texture, stratigraph stratigraphic ic and structural features, and fractures. The The FMI bu button ttons s prod roduce only only a profile of the conductivity—the response correlates with with the forma formation conductivity, rather than an actual conductivity/resistivity tivi ty measurem easurement. ent. This is because because the high- and and low-resoluti low-resolution on components components are generally similar in magnitude and impossible to separate separate.. The T he button response is typically scaled to present
a resistivity curve that coincides with the shallow laterolog over distances that are large in comparison with the FMI electrode spacing. Over comparatively short distances, the scaled curve provides a high-resolution, but approximate, resistivity log. The The res resolutio olution n of the the FMI too tooll is the button size at 0.2 in. In theory, this means that an object larger than 0.2 in. appears as its true size. An object smaller than 0.2 in. may be visible, depend depending ing on the resistivi resistivity ty contrast with the background rock. If it is visible, it may appear to be as large as 0.2 in. In conformance with sampling theory, the FMI image is sampled at one-half the resolution (0.1 in.) vertically and horizontally so that the theoretical resolution is not compromised. To achieve 0.1-in. sampling horizontally for the button diameter of 0.2 0.2 in., the buttons are arrange arranged d on the pad and flap in two horizontally offset offset rows. rows.
FMI measurement current path.
Upper Upper electrode electrode
M ass insulated sub
Current
Lower electrodes
Characterization of rock structure FMI imag images provide provide critical critical inform i nformat ation ion if the rock structure and sedimentary features are significant determinants |of formation productivity. The figure below shows paired carbonates and sandstones with the same porosity but completely completely diff differen erentt permeabilities abili ties and hence production capabilities.
FMI images differentiate the structures that result in vastly different production potential for formations with the same porosity.
Collapse Breccia (14% porosity, 6000 BOPD)
2 ft
Vuggy Limestone (14% porosity, 0 BOPD)
4 ft
Slumped Sandstone (18% porosity, poros ity, 0 BOPD) BOPD)
1.5 ft
Tur Turb bidit idite e Lev Levee Deposi epositt (18% porosity, 5000 BOPD)
1.5 ft
Net pay determination in laminated sediments The The FMI tool is the prefe referr rre ed approa roach for determining net pay in the laminated sediments typical of fluvial and turbidite turbidite depositi depositiona onall envir environm onmen ents. ts. The The method for for obta obtain inin ing g an accu ccurat rate sand count is to compute an average resistivity curve from the FMI measurements and apply a cutoff that
distinguishes sand from shale. Laminations as thin as 0.2 in. can be resolved. resolved. Sections with wi th lam laminations thinner than this intrinsic resolution are analyzed by calibrating FMI lithofacies with the sand count from core. The The res resultin lting g sand-shale curv curve e can can be analyzed for the bed-thickness distribution and used to derive mappable parameters.
In highly laminated sediments, the FMI log clearly shows the net pay zones that can contribute to production.
Gamma Ray
Neutron Porosity
20 (gAPI) 120
0
Caliper X 5
(in.) Caliper Y
5
(in.)
60-in. AIT Resistivity 15
0.2
(ohm-m)
20 0
(p.u.)
60
Density Porosity (p.u.)
60
Depth 20-in. AIT Resistivity Sonic Porosit P orosity y 1:48 15 (ft) 0.2 (ohm-m) 20 0 (p.u.) 60
XX10 250
XX20 260
XX30 270
Sand
FMI Image Image Horizontal Horizontal Scale: Scal e: 1:9 Orientation North 0 Resistive
120
240
Shale
360 Shallow FMI Resistivity Resistivity
Conductive
0.5
(ohm-m)
5.5
Visualization of sedimentary features The The inte interp rpre reta tattion of ima image-derive rived sedimentary dip data enables the visualization of sedimentary structures that define important reservoir geometries tries and and petrophysical petrophysical reservoir reservoir parameters. The figure to the right shows eolian dunes separated by interdune deposits.
FMI images and dip data clearly differentiate the dune and interdune deposits. The data were 1 2 -in. diameter borehole. acquired from an 8 ⁄
720
730 Interdune 740
750 Dune 760
770
780
Interdune
790
Fracture permeability direction The The princi rincip pal stres ress azimu imuths obtaine ined from borehole image analysis define the maximum permeability direction in fractured reservoirs. The fracture set that is aligned with the maximum horizontal stress contains the widest fracture apertures and dominates the direction of fracture permeability. The The stylolit lolite e that appears as a dark, rk, irregular feature in the center of the image to the right acts as a vertical permeabil eability ity barr barrier. ier.
FMI data analysis identifies the maximum permeability direction in a fractured reservoir, which is important information for designing a completion for optimal production.
Fracture aperture (mm) Azimuth 180
°
Maximum horizontal stress
3 ft 90
°
Minimum horizontal stress
0
°
.0001 0.001
0.01
.01
50 Dip 90 °
°
0.1
0
Structural interpretation Well-to ll -to-we -well ll correlation correlation is i s difficult difficult in deviated wells with sections of steep and varying structural dip. The The struct ructu ural ral inte interp rpre reta tation tion of seisismic sections is greatly improved by the use of high-quality bedding dips to compute accurate logs of the true stratigraphic thickness (two well logs
second from left in the figure below). The The two two corre correla late ted d wells wells are plotte lotted on the seismic section using structural dip (magenta lines) and stratigraphic markers (cyan lines). The ramp anticline is well defined by the well data compared with the seismic section. The far-right plot in the figure compares the thickness of strati-
graphic intervals 1 through 37 in both wells. The thicknesses are the same in interval A, but from stratigraphic marker 13 to marker 27, the layers in Well 2 show increa increasing sing thicknes thickness s in in comparison with the layers in Well 1, indicating a syntectonic sedimentation differential. differential.
FMI images and dip data are an independent complement for structurally interpreting seismic sections. The ramp anticline is better defined by the dip data than the seismic surface data.
A A: Equal layer thickness in both wells B: Layer 20% thicker in inWell Well22
Well 2
B
Tru True e stratrgraphic layer thickness Tru True e stratrgraphic layer A thickness Start of folding
A Well 1
Distorted zone
Well 1 B
A Start of folding 1
37 36
13 1
37 36 27 27
1.5 km 13
1
13
1
1.3 km (Scale 1:1) 1.3 km (Scale 1:1)
27 13
36 27
37 36
37
Three-dimensional reservoir modeling Once the structural framework is established within the geology and geophysics eophysics workfl wor kflow, ow, the reservoir reservoir is divide divided d into lithologic l ithologic units, which are then populated with properties such as porosity, permeability and water saturation to support reservoir simulation. The lithologic units are created created determ determini inisticall stically y or stochastistochastically. The latter approach is shown
in the figure below and employs the Fluvial Simulation (FLUVSIM) methodology. Sand-shale logs can be derived from wireline wireline and and log l ogg ging-whil ing-whilee-dril drilli ling ng (LWD) logs from vertical as well as horizontal horizontal wells. Criti Critical cal guidance guidance for stochastic modeling of the sand-shale distribution is provided by the geological information derived from FMI borehole images. Crossbedding translates
into channel directions, and FMI images ages superbly define channel channel heights in amalgamated units. Other variables, such as the channel width and channel sinuosity, can be estimated using geological analogs based on detailed sedimentological analysis of FMI image data in conjunction with other log logs s and and core data. data.
The three-dimensional display shows the distribution of sand (orange) and shale (blue) as modeled for a fluvial reservoir using FMI-derived 1 2 -in. sedimentological information in an 8 ⁄ -in. well.
N Crossbed dip-azimuthal histogram
W
E
S
E
3 ft
Shale San San
Key input for Mechanical Earth Models A growing application for borehole images is providing input and verification data for the Mechanical Earth Model (MEM) used to optimize well construction. Better Better understand understanding ing of borehole stability can save operators millions of dollars by shortening
the learni learning ng curve duri during ng the initial ini tial field development. The The exam xample below low shows the the bore orehole breakout and hydraulic hydraulic fractu fractures res and their relationship to the horizontal stresses. An MEM can predict the type and position of induced features on borehole images. Disagreement
between model modeled and observed observed fea fea-tures on the borehole images is used to tune the assum assumptions made in the MEM, such as changing the azimuth or relative magnitude of the principal stresses.
A Mechanical Earth Model can be used to predict the type and position of drilling-induced features in the borehole. Knowledge of the directions and relative magnitude of the principal stresses is needed to optimize a drilling program.
Minimum horizontal stress
3 f
Borehole breakout Induced fracture
FMI tool string. string.
FMI Specifications A ppl i cat i ons
St r u c t u r a l g e o l o g y, s t r a t i g r a p h y, r e s e r v o i r a n a l ys i s, heterogeneity, heterogeneity, fine-scale features, real-time answers
Ve r t i c a l r e so l u t i o n
0 .2 i n . w i t h 5 0 - m i cr o n f e a t u r e s vi si b l e
A zi m u t h a l r e s o l u t i o n
0 .2 i n . w i t h 5 0 - m i cr o n f e a t u r e s vi si b l e
M e a su r i n g e l e ct r o d e s
192
Pa d s a n d f l a p s
8
Co v e r a g e
8 0 % i n 8 - i n . b o r e h o l e (f u l l b o r e i m a g e m o d e )
M a x p r e ss u r e
2 0 ,0 0 0 p s i
M ax t em per at ure
3 5 0 °F [1 7 5 °C]
Borehole diameter Borehole M in
7 8 in. 5 ⁄ in .
M ax
21 i n.
M a x h o l e d e vi a t i o n
90°
Logging speed Fu l l b o r e i m a g e m o d e
1 ,8 0 0 f t / h r w i t h r e a l - t i m e p r o c e ss e d i m a g e
Fo u r- p a d m o d e
3 ,6 0 0 f t / h r w i t h r e a l - t i m e p r o c e ss e d i m a g e
D i pm et er m ode
5 ,4 0 0 f t / h r w i t h r e a l - t i m e d i p p r o c e ss i n g
In c l i n o m e t e r m o d e
1 0 ,0 0 0 f t / h r
M a x m u d r e si st i v i t y
50 ohm -m
FM I tool M ax di am et er
5 i n.
M a ke u p l e n g t h
2 4 .4 f t
M a ke u p l e n g t h w i t h f l e x j o i n t
2 6 .4 f t
W ei ght i n ai r
4 3 3 .7 l b m
Comp ompres ressio sional nal stre streng ngth th (TL (TLC C* opera operation tions) s)
12,0 12,000 00 lbf lbf (safe (safety ty facto factorr of 2)
M a x p a d p r e s su r e
44 l bf
Co m b i n a b i l i t y
To p co m b i n a b l e w i t h o p e n h o l e w i r e l i n e t o o l s
24.4 ft
Pad section (1.3 ft) Too Tooll zero ero (0 ft) M aximum aximum tool tool diameter 5 in.
www.connect.slb.com SM P-5822
©Schlumberger
April 2002
*M ark of Schlumberger
