CC BY
73
short communication Doi: https://doi.org/10.18599/grs.20183.261-266
An example of practical application of information on fracturing according to the well logging data complex
and high-tech methods
R.N. Abdullin, A.R. Rakhmatullina*
TNG-Group LLC, Bugulma, Russian Federation
Abstract. In the article the issue of investigation by logging methods of reservoirs with natural fracturing is considered. A special case of revealing the reason for fast watering of productive layers with the help of a logging data complex and high-tech methods, such as: cross-dipole acoustic logging, acoustic scanner, electric micro-imager is considered. Scanners allow us to get an image of the inner surface of the well wall in order to reveal fractures. Measurement of the propagation characteristics of acoustic waves is used to detect fractures. Complex interpretation led to the conclusion that the watering is due to the presence of sub-vertical fractures associated with the underlying aquifers.
Keywords: fracture, microscanner, watering
Recommended citation: Abdullin R.N., Rakhmatullina A.R. (2018). An example of practical application of information on fracturing according to the well logging data complex and high-tech methods. Georesursy = Georesources, 20(3), Part 2, pp. 261-266. DOI: https://doi.org/10.18599/grs.2018.3.261-266
There are several approaches to identification and investigation of reservoirs with natural fracturing. Out of these approaches, the following deserve closer attention (Dobrynin et al, 2004):
- lost circulation and growth of ROP during drilling are the main indicators that drilling is going on in a fractured and porous medium;
- fractures and core solution channels provide direct information on the nature of reservoir's porosity. If actual flow rates of a formation are several times higher than those estimated with core data, then we should suspect presence of natural fractures in such a formation not observed on core samples. A low core delivery rate -less than 50% - also presumes presence of a strongly fractured carbonate rock in the core sampling interval;
- logging tools are designed in such a way that their readings are variously affected by different features of a borehole and a section. Well Logging methods based on measurements of acoustic waves propagation characteristics are used for identification of fractures. Caliper logging data, density logging and electrical logging data in certain circumstances may be useful for identification of fracture zones;
- pressure build-up curve analysis;
- vertical fractures in a non-deviated hole may be
*Corresponding author: Aniya R. Rakhmatullina E-mail: [email protected]
© 2018 The Authors. Published by Georesursy LLC This is an open access article under the CC BY 4.0 license (https://creativecommons.org/licenses/by/4.0/)
identified as high-amplitude anomalies intersecting other bedding planes;
- fractures and solution channels are discovered with methods for direct or indirect imaging of borehole walls applying a borehole imager;
- abnormally high production rate is typical of naturally fractured formations;
- a significant growth of a Well's productivity after hydrochloric acid inflow stimulation is a reliable indication of a formation with natural fracturing. Acid treatment is conducted in order to expand fractures and channels;
- due to high permeability of fractures, pressure's horizontal gradient in a fractured formation is generally not high, both near the well and over the entire formation.
Table 1 shows the methods, and their capabilities and limitations in identification of fractures. It is obvious that the most effective instruments for assessment of fractures are acoustic and electrical micro imagers.
The oilfields of TPP "TatRITEKneft" of Nurlat Group showed flooding of productive horizons during development. In order to establish causes of fast flooding, it was decided to apply an extended set of Well Logging methods, including high-tech investigations. Fracture studies in Mid and Lower Carboniferous deposits were conducted in two wells: No. 1426 (crestal) and No. 1429 (flank). Their location is shown on Fig. 1 of a structure map for top Tournaisian stage. The entire completed set of Well Logging methods was analyzed, including electrical micro imager (MCI), cross-dipole acoustic log
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Core Electrical Formation Imagers (FMS\FMI\MCI) Acoustic Borehole Imager Litho-Density Log Lamb-Stoneley Wave Lost Circulation
What is identified? Local fracture porosity Mud penetrating fractures Contrasting acoustic properties Density of hard mud particles penetrating the fractures Stoneley wave energy reflected by fractures Loss of circulation from borehole into formation through fractures
How narrow are the fractures to be identified? Approximately several micro meters Approximately several micro meters in case of sufficient conductivity contrast 1 mm 5 mm 1 mm 0.2 mm
Man-made fractures mistaken for natural permeable fractures Fracture porosity. Man-made fractures. Fracture porosity. Man-made fractures. Formation damaged while drilling Fracture porosity. Man-made fractures. Interlayers with high impedance values and part of healed fractures Fracture porosity. Formation damaged while drilling. Salinity. Boundaries of cavern No
Survey depth Core diameter 10 mm 3 mm 100 mm Less than 1.8 м Mud penetration radius is >1 m
Can data from this method be used to establish fracture's dip angle and bedding plane angle? Yes Yes Yes No No No
Mud limitations No Only water-based mud Mud density must be less than 1.68 gr/cm3 Mud density must be 1.2 gr/cm3 No No
Remarks No core delivery from highly fractured «corrugated zones» Hard to differentiate fractures with high and low permeability Hard to differentiate fractures with high and low permeability No Fractures clogged with mud's hard particles are often not identified Provides information on the level of formation damage and requirements to its treatment
Table 1. Brief characteristics of natural fractures investigation methods (according to Mukhamadiev et al, 2014)
(MPAL) and acoustic scanner (САС) in order to identify fractures which contribute to Well flooding.
Figures 2, 3 show interpreted data from the extended Well Logging set of methods. The second track after depth column on Figure 2 shows Gamma-Ray curve, Caliper Log and Neutron Gamma-Ray Log, Gamma-Gamma Density Log curves; the third track shows Nuclear Magnetic Log; the fourth one - electrical metering; the fifth track shows porosity and oil saturation coefficients; the following columns show fractured intervals identified due to various Well
Logging techniques, including anisotropic intervals identified after Cross-Dipole Acoustic Logging (tracks 8-10). The right-hand side of the Figure shows Cement Bond Log data, string contact, Variable Density Log (string bond and rock bond). Identified fractured intervals are confirmed by deterioration of the casing string's cementing quality identified during another acoustic survey in a cased hole (Fig. 2b), as well as by further fast flooding of productive reservoirs.
Well 1426 in the 951.0-1035.0 m interval (Vereiskian-Bashkirian) after electrical micro imager identified 13
Fig. 1. Structure map for top Tournaisian stage
healed fractures, 8 partially-healed fractures and 3 open fractures. The 1196.5-1295 m interval in total showed 20 healed fractures, 14 partially-healed and 4 conductive fractures. The fracture dip angle was predominantly 45.2-74°.
According to acoustic logging data, in well 1429 five healed fractures were identified in the 1188.6-1222.4 m interval. The fracture dip angles vary within 65.8-71°, the dip azimuth is within 91-115.6° range (south-east being the main dip direction).
An example of a fractured interval as per electrical micro imager data is shown on Figure 4.
Well 1429 located at the flank of the structure, according to high-tech methods identified much less fracture intervals. Fast flooding is most likely to be caused by presence of sub-vertical fractures associated with underlying aquifers. The cause of Well flooding is in presence of natural fracturing of rocks.
Therefore, high-tech methods identified a reason of fast flooding which is associated with natural fracturing of sub-vertical trend.
Oil-saturat. Water-saturat. Water-oil-saturat. Porous Vuggy Fractured Porous-vuggy
wsA ¡.----------I mmv
Porous-fractured Not evaluat. Clayey reservoir Consolidated reservoir
GК (MKP/H)
0 20 40 60 80
0 4 8 12 16
NGK (ycn.eg.)
0.6 3 5.4 7.8 10.2
0.6 1.8 3 4.2 5.4
2.2 rrxn 2.4 2.6 2.8
150 250 1 DTC 350 , 1 , 450 I 550
mkc/m DS, mm
196 236 276 316 356
U1, ue 500 1000
Pvp*rv
U2, ue 0 500 1000 0
IK (Омм) 10 20
U3, ue 0 500 1000 1
BК (Омм) 10 100 1000
V/V KpAK
0 0.1 0.2 , 1 , 1 Kn TP 0 0.4
V/V Kp 0 0.1 0.2 , 1 , 1
PHIT-S 0 40
p.u. Kgl 1 0.6 0.2 0 , 1 , 1 Pu Kp tr 0 0.4
p.u. Kp MPAL 0 0.1 0.2 , 1 , 1 % Dkv -1 '
Kn rrKn 0 0.1 0 2 Dtr -1 '
I.
Fig. 2. Analysis offracturing for well 1426 in Lower Carboniferous deposits: a) open hole, b) cased hole
8CIEf>
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KH_MAT 0.1 0.2
Kgl
0.6 0.2 0
0.2
0
20
Fig. 2. Analysis offracturing for well 1426 in Lower Carboniferous deposits: a) open hole, b) cased hole
Water-saturat.
Porous-vuggy
wrm
Porous-fractured
NGK (ycn.efl.)
0.6 3 5.4 7.8 10.2
0.6 1.8 3 4.2 5.4
GK (MXP/H)
0 25 50 75 100
0 5 10 15 20
r»r»r»r<i
Water-oil-saturat. Clayey reservoir
Vuggy
Y77771
Fractured
a)
Consolidated reservoir
DS, mm 276
IK (omm) 10 100 1000
MT3, Omm 0 5
BK (Omm) 10 100 1000
Mn3, Omm 0 5
0 Kp 0.2 0.4 , 0.6
fl.e.
Kp mpal
0 0.2 0.4 , 0.6
0 fl.e. NPHI 0.2 0.4 0.6
Fig. 3. Analysis offfracturing for well 1429 in Lower Carboniferous deposits: a) open hole, b) cased hole
Porous
Not evaluat
Pp
Dkv -1 1
DTC
150 250 350 450 550
-1 1
Water-oil-saturat.
Not evaluat.
Y7777\
Fractured
Water-saturat. Porous-fractured
b)
Clayey reservoir
Consolidated reservoir
MARK 2
2.6 4.65.6 -10
GK (MKP/H)
8 16 20 -10
DS, mm
236 27(296 -10
SPEED, m/h 1500 212000
M/^ac A1AC, db 10 30 ALAC, db/m 10 30 40
2
Fig. 3. Analysis offracturing for well 1429 in Lower Carboniferous deposits: a) open hole, b) cased hole
Fig. 4. Example of a fractured area according to electrical micro imager data
Vuggy
900
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References
Dobrynin V.M., Vendel'shtein B.Yu., Kozhevnikov D.A. (2004). Petrophysics (physics of rocks). Moscow: Neft' i gaz Publ., Gubkin RSU of oil and gas, 368 p. (In Russ.)
Mukhamadiev R.S.1, Dubrovskiy V.S.1, Abdullin R.N.1, Rakhmatullina A.R.1, Polushina D.A.1, Diukova M.M. (2014). Study of Rock Fracturing through the Application of Electric and Acoustic Imagers. Neft, Gas, Novacii, 2(181), pp. 10-13. (In Russ.)
About the Authors
Rinat N. Abdullin - Head of the Geological Department, Directorate of Science and Technology
TNG-Group LLC
Nikitin st., 12a, Bugulma, 423232, Russian Federation
Aniya R. Rakhmatullina - chief Geophysicist of the Geological Department, Directorate of Science and Technology
TNG-Group LLc
Nikitin st., 12a, Bugulma, 423232, Russian Federation E-mail: [email protected]
Manuscript received 08 June 2018;
Accepted 05 July 2018; Published 30 August 2018
