TECHNICAL FEATURES AND APPLICATIONS OF FMS TOOL, FMI TOOL, DSI TOOL FOR a 1x WELL, BLACK LION FIELD, CUU LONG BASIN

Electrical borehole image measurement and display...11 2.. FMS tool Formation MicroScanner: FMS Formation MicroScanner, first electrical imaging tool, as an evolution of their SHDT dipm

HO CHI MINH CITY NATIONAL UNIVERSITY

UNIVERSITY OF SCIENCES GEOLOGY FACULTY

black lion field, CUU LONG BASIN

INSTRUCTOR : MASTER PHAN VĂN KÔNG

STUDENTS:

H TH H NG VÂN Ồ THỊ HỒNG VÂN Ị HỒNG VÂN Ồ THỊ HỒNG VÂN 0816582

NGUY N MINH NH T ỄN MINH NHỰT ỰT 0816341

PHÙNG TR N TR NG TH C 0816489 ẦN TRỌNG THỨC 0816489 ỌNG THỨC 0816489 ỨC 0816489

TR N CÔNG B NG 0816038 ẦN TRỌNG THỨC 0816489 ẰNG 0816038

HỒ CHÍ MINH CITY – DECEMBER 2011

I TECHNICAL FEATURES OF FMS TOOL, FMI TOOL AND DSI TOOL 3

I.1 FMS tool (Formation MicroScanner) 3

I.2 FMI tool (Formation MicroImager) 6

I.3 DSI tool (Dipole Sonic Imager) 9

II APPLICATIONS OF FMS TOOL, FMI TOOL 11

II.1 FMS tool

1 Electrical borehole image measurement and display 11

2 Constructing lithostratigraphies 14

3 Grain size changes 16

4 Fractures and faults 16

5 Core orientation and stress measurements 19

II.2 FMI Tool 21

1 Feature identification and dip and azimuth measurement 21

2 Structural unconformities 22

3 Slumps 23

III APPLICATIONS FOR A-1X WELL, CUU LONG BASIN 25

III.1 Fractures Classification 25

1 Cementitious fractures 25

2 Fractures filled up with conductive materials 25

3 Fractures made during drilling process 26

III.2 How to interprete Stoneley wave with DSI equipment? 26

III.3 Fractures analysis for A-1X well, BLACK LION field based on FMI and DSI equipments 26

REFERENCES MATERIALS 34

I TECHNICAL FEATURES OF FMS TOOL, FMI TOOL AND DSI TOOL

I.1 FMS tool (Formation MicroScanner):

FMS (Formation MicroScanner), first electrical imaging tool, as an

evolution of their SHDT dipmeter.The FMS tool consists of four orthogonalimagingpads eachcontaining 16microelectrodes which are in direct contactwith the boreholewallduring the recording.The button current intensity is sampledevery 0.1 in (2.5mm).The tool works byemitting a focused current from the fourpads into theformation The currentintensity variations are measured by thearray of buttons on each

of the pads

Fig.1: FMS tool Fig.2: FMS operating structure

The first tool only provided an image of 20% of an 8.5” borehole, using justtwo pads Since then there has been steady progress in borehole coverage(Bourke,1992) and tool technology The present tool, the Full-bore Formation

MicroImager (FMI) providesnearly 80% coverage in an 8.5” diameter borehole of

high quality images

Tectonic, sedimentary and diagenetic features usually recognized onborehole images

How to interpret the RAB, FMS/FMI images

FMI tool (Formation MicroImager):

FMI consists of four pads on two orthogonal arms like the dipmeter, but inthe imaging tool, the four pads each have a hinged flap so as to extend the area ofelectrical contact Pad faces are curved to match borehole curvature and areapproximately 8 cm (3.2”) wide and 18 cm (7”) long; flaps are 8 cm (3.2) widebut only 6 cm (2.5”) long Both pad and flap have arrays of 24 button electrodes

In order that the pads and flaps maintain contact with the formation, theyare free to tilt independently of the tool body Thus, when the tool is not parallel

to borehole wall, as frequently occurs in horizontal and highly deviated wells, thepads still remain in contact In addition, the tool uses hydraulic self-centering toimprove pad contact, especially in horizontal wells, where the usual pad leafspring are not adequate

The unique design elements of the FMI are the pad and flap and electrode

array Pad and flap are both conductive and have inset, 24 individually insulatedbutton electrodes, arranged in two rows of 12 Individual buttons are 0,5 cm(0,2”) apart and the two rows are separated by 0.75cm (0,3”) The buttons of one

row are offset 0,25 cm (0,1”) vertically compared to the other The top row ofbuttons on the pad is 14,5 cm (5,7”) above the top row of buttons on flap Whenthe tool is used with the flap, 192(8x24) button samples are recorded at everydepth sample point around the borehole The tool may also be run in four-padmode when 96(4x24) button samples will be recorded.

electrode s

Logging speed Hole diameter

Fig.2: Pad assemblage and sensor detail from the Schlumberger FMI tool

Two types of image color designation are possible, one in which the colorrange covers a population representing the entire log dataset, called “staticnormalization”, and one in which the sampled population is a screenful (orsimilar limited quantity) of data values, when it is called “ dynamicnormalization” Using static normalization, intervals (formations) with similarelectrical properties will be relatively similar throughout the log However, muchdetail will be lost, especially in zones of very high values such as may be found inhydrocarbon bearing reservoirs The detail may be recovered by using dynamicnormalization Even at overall high values, small variations will be sufficientbecause a color code change since the entire population sample itself has highvalues However, with a dynamic normalization, similar lithologies may beappear different through the one log The two processing are complementary.Dynamic normalization is generally best for detail workstation interpretation;static normalization is conveniently used for whole well analysis, and whole wellhard copy, especially at compressed vertical scales when detail is inevitably lost

Image resolution and identification: The resolution of individual FMI

buttons is indicate at 0.2” (0.5 cm) which is also the effective electrode size.Signal penetration is around 1.4 cm but varies However, in terms of the images

produced, because of tool design and log sampling rate, the formation is sampledhorizontally and vertically every 0.1” (0.25 cm) Pixels of 0.1”x 0.1” (0.25 cm x0.25 cm) are used for image creation, that is, half the individual electroderesolution Features the size of a pixel will not be resolved and not be separated.Features smaller than a pixel will appear pixel sized When considering theimages themselves it is the ability to be able to recognize an object which isimportant.

Fig.3: Comparison of real thin bed thinness from core and estimated bed thickness from electrical images Sands were relatively more resistive than shale.

Some notion of the practical possibilities of log use can be gained fromwork on bed resolution This shows that shoulder effects are important.Schlumberger found that the FMS tool would resolve the thickness of sand beds

in a sand/shale turbidity sequence, down to 5 cm accurately For sand bedsthinner than this, interpretation of the electrical image gave an exaggeratedthickness and a corresponding under-estimate of shale bed thickness However,thin turbidity sands have been recognized down to 2.5 cm At an even finer scale,below tool and image resolution, fine lamination can be recognized but in ageneral sense rather than each lamina being identified

For irregular, at very small scale, shoulder effects are likely to merge anddominate and render identification difficult or impossible.

I.3 DSI tool (Dipole Sonic Imager):

The DSI* Dipole Shear Sonic Imager com-binesmonopole and dipole sonic acquisition capabilities.The transmitter section contains a piezoelectricmonopole transmitter and two electrodynamicdipole transmitters per-pendicular to each other Anelectric pulse at sonic frequencies is applied to themonopole transmitter to excite compressional- andshear-wave propagation in the formation ForStoneley wave acquisition a specific low-frequencypulse is used The dipole transmitters are also driven

at low frequency to excite the flexural wave aroundthe borehole The tool is made up of three sections-acquisition cartridge, receiver section, andtransmitter section An isolation joint is placedbetween the transmitter and receiver sections toprevent direct flexural wave transmission throughthe tool body The receiver section has an array ofeight receiver stations spaced 6 in [15.24 cm] apartand 9 ft [2.74 m] from the monopole transmitter, 11

ft [3.35 m] from the upper dipole transmitter, and11.5 ft [3.50 m] from the lower dipole transmitter.Each receiver station consists of two pairs ofwideband-piezoelectric hydrophones aligned withthe dipole transmitters Summing the signalsrecorded by one pair of hydrophones provides themonopole waveform, whereas differentiating them cancels the monopole signal

and provides the dipole Fig.4: DSI tool waveform When a

dipole transmitter is fired, the hydrophone pair diagonally in line with thetransmitter is used Four sets of eight waveforms can be acquired from the fourbasic operating modes fired in sequence A special dipole mode enablesrecording both the inline and cross line (perpendicular) waveforms for eachdipole mode This mode, called both cross receivers (BCR), is used for anisotropyevaluation The optional S-DSI modification to the DSI tool uses a special slow

sleeve to extend the slowness measurement to 1,200 ms/ft [3,937 ms/m] from

II APPLICATIONS OF FMS TOOL, FMI TOOL

II.1 FMS Tool:

1 Electrical borehole image measurement and display:

In the past decade, logging tool developments have enabled the simultaneousacquisition of multiple closely spaced micro-resistivity logs which may bepresented as visual images (Fig I) reflecting variations in the electricalconductivity of the rock on the millimetre scale These electrical images, whilstnot equivalent to optical images provide the geologist with an opportunity toview the subsurface formations in their complete state and in effect "to carry outfield mapping of the ocean crust

Figure 5 Demonstrates schematically the FMS tool in the borehole and how a

single pad provides a series of current intensity versus depth curves which arethen converted into a strip-like image of the borehole wall The current intensity

is convened to variable intensity grayscale or colour images through a series ofprocessing steps These correct for variations in the focusing current, speed oftool movement up the hole and localized differences in response betweenelectrode buttons The resulting image is then statically normalized such thateach grey level is represented by an equal area on the final image This produces

a large-scale visualization of the data which unfortunately may mask importantfine details This may be overcome by the use of dynamic normalization whichattempts to enhance such localized features through contrast magnification

within a sliding window The choice of window size is critical here in that it must

be larger than the smallest feature of interest but smaller than the thickness ofthe unit being investigated An alternative means of enhancing the image isthrough histogram equalization in which the entire grayscale is used within asliding window this works well when there is no electronic noise in the data

Processed images may be presented as an intact borehole image on aworkstation or as an unrolled view of the (flattened) borehole In the latter casethe borehole image is effectively cut open along its length and presented as fourseparate strip images: each is orientated with respect to north based oninclinometry measurements made during the tool's ascent up the borehole.Physical distortion of the images will occur unless the horizontal and verticalscales are equal This is an important aspect to consider when interpretation ofdetailed sedimentology or textural-based features is required Thus the flattenedimages are displayed as four separate strip-like images (see Fig 2) In assessingthe images convention dictates that in grey scale images black represents moreconductive with white more resistive which translates to brown/black(conductive) and white/yellow (resistive) for most colour image schemes

Fig.6: Downhole electrical images of turbidite sequences in the lzu-Bonin are

(ODP Hole 792E, Leg 126): white/yellow indicate coarser-grained, more resistivesediments, orange/brown finer-grained, more conductive sediments

As an example, sandstone intervals containing salt water tend to givesvertically consistent electrical responses in the same formation Once identified,the salt water sandstones are seen to have it distinct and diagnostic electricalimage response (Fig 2).

Fig.7: Example of the bed resolution of the electrical image logs in thin-bedded

gravity deposit (salt water fluids) image provide an improved net-to-gross ratiocompared to the standard logs (a) image log interpretation, (b) standard log

interpretation, FMS image using dynamic normalisation, 5m window, darkcolours indicate higher resistivity.

Fig.7: Sandstone grain size grading reflected in the electrical image log colour

changes in the hidrocacbon zone (arrows indicate fining-up) the darker shadesindicate a higher volume of irreducible hydrocacbon (Hirr) as a result of lowerpermeability higher permeability sands are flushed The subtle responses arebrought out best using a 5m dynamic normalization window Shales are seen aslighter shades that is lower resistivity (compare to Fig.2, shale and sandresponses in salt water bearing formation

electronic conductors such as pyrite which effectively short-circuit theelectrical paths through the pore space Using FMS images it is thuspossible to construct a continuous lithostratigrtphy for the borehole evenwhere there is disparate core recovery

3 Grain size changes:

Electrical image logs can only be used to imply grain size variations wherethere is an associated change in permeability affecting the electrical properties ofthe formation (cf.Prosser et al 1995) Variations in permeability are associatedwith differences in the depth of invasion of drilling mud filtrate which createdifferences in fluid resistivities close to the borehole High permeability generallyallows greater flushing and filtrate invasion while low permeability, at least in ahydrocarbon zone is associated with higher irreducible hydrocarbons (oil).Electrical images are affected by these near-hole, fluid resistivity changes Asecond grain size related property which also affects electrical behaviour is claycontent liner grain sizes tending to have it hither clay volume The two effectswork to some extent in parallel

Changes in near-hole fluid resistivity are best seen in hydrocarbon hearingintervals where the electrical images are responding to the formation justbeyond or through the flushed zone In lower permeability zones where there is ahigher volume of unflushed (irreducible) hydrocarbon,, image colour shovehigher resistiyities (dark colour, in the figures) These lower permeability zonesare associated with finer grain sizes The better permeability associated withcoarser grain sizes shows as lighter shade where the hydrocarbons have beenflushed (Fig 4) The clarity of these variations depends on the choice of imageprocessing parameters and changes in dynamic window length are critical (Fig.4)

In water zones, gradual changes in image colours are more likely to beassociated with change in clay content themselves linked to variations in grainsite (finer grain site more clay) working in parallel The presence of clay clog thepore spaces, decreases permeability and increases formation resistivity sogiving darker shades, The effect are seen in some of the thinner sandstones of theHeimdal Formation but the changes are often subtle and difficult to detect