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SPE-187682-MS
Successful Hydraulic Fracturing Techniques in Shallow Unconsolidated
Heavy Oil Sandstones
E. Zagrebelnyy, M. Martynov, and A. Konopelko, JSC, Messoyahaneftegas
Copyright 2017, Society of Petroleum Engineers
This paper was prepared for presentation at the SPE Russian Petroleum Technology Conference held in Moscow, Russia, 16-18 October 2017.
This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents
of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect
any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written
consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may
not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.
Abstract
This paper describes succesfull experience of implement hydraulic fracturing at unconsolidated lowtemperature formation in Yamal region in Russia. Experience of hydraulic fracturing as known as well
stimulation method for deep-water deposits of West-Siberian oil an gas basin. Hydraulic fracturing at
terrestrial deposits, which is Vostochno-Messoyakhskoye field, are not used in general practice. There are
few reasons for that: shallow depth (about 800m), incompetent rock, gas-cap and oil-water contact have
to limit fracture height, low formation temperature (16°C) doesn't available to use traditional oxidezing
breakers and resin-coated proppants. But the other hand high viscosity of oil (111CP) promotes to using
hydraulic fracturing for increasing coverage ratio at exploration of high-stratified formation. All these points
are signing that classic hydraulic fracturing techniqes are not applicable for this facility.
The basic development technology is the drilling of horizontal wells with a length of 1000m, equipped
uncased liners with filters (both premium and perforated pipes). However, as the first results of drilling and
development of wells of full-scale development showed the extraction of reserves located in a highly divided
reservoir is a laborious process and requires the attraction of new technologies of drilling, completion and
production stimulation.
There was developed pilot project of implement hydraulic fracturing technology to directional wells for
subsequent replication to horizontal wells using specialized completion systems. This article describes the
implemented program of pilot work on directional wells and a set of accompanying surveys, also provides
conclusions and plans for further replication to horizontal wells with the transition to multi-stage fracturing
technology.
Introduction
Because of a large amount of reserves (more than 80%) of the main production target belong to high
dessicated formation, so it was required to develop and implement technological solutions for fracturing
operations on a weakly consolidated heavy oil reservoir, with gas cap and underlying water. In the world
practice, hydraulic fracturing of the reservoir at similar formations is found only in foreign deposits. For
example, there is an experience of successful hydraulic fracturing at the Prudhoe Bay, Kuparuk [2]. These
are oil and gas fields in the area of the northern slope of Alaska. The technology of hydraulic fracturing
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SPE-187682-MS
is the use of proppant treatment with epoxy resin. The treatment of proppant with epoxy resin allows to
bond the proppant, forming a high-strength frame of fracture, which increases fracture conductivity, also
natural gravel packing inside the frame is formed, which prevents sand production. By results of application
it was revealed that the average productivity of the well increased by 230%. The main negative aspect of this
technology is high costs and the need for detailed design of the event [2]. Also technology of limiting the
breakthrough in water layers (tip screen out) is used to high-permeability reservoirs in Brazil and Colombia
[3]. The main idea of this method is to create a short high-conductive fracture (with hign hydraulic width),
and maximizing dimensionless fracture conductivity (FCD) in a high-permeability reservoir. According to
the results of testing, the efficiency of this technology is up to 200% [3].
In described case, there is a combination of complicated factors that are typical for various examples of
fracturing technology implementation at similar formations. Thus, for solving current problems, an urgent
and knowledge-intensive task was set to learn how to succesfull launch the hydraulic fracturing technology
in directional wells (first stage of pilot program) and modify lessons learned to multi-stage fracturing in
horizontal wells (second stage of pilot program). As a result, it was planned to solve a number of applied
problems, such as:
1. Solving the problem of high directional properties of formation. Low starting rates of the basic
technology (horizontal well with 1000m horizontal section) in the highly dissociated cyclite B are
due to incomplete coverage of the productive thickness. It is possible to involve more sublayers in
exploration with hydraulic fracturing in comparison with a conventional horizontal well.
2. Removing the damaged zone of the formation. Increasing of effective well radius due to fracture
making through to zone contaminated by mud filtrate. The average depth of penetration of the mud
filtrate is 30-40 cm, the calculated fracture length is 25-50 m.
3. Well stimulation. The main uncertainty of the alluvial flat part of the cyclite B is the permeability (the
petrophysical and hydrodynamic dependences are overestimated with respect to core studies). Value
of dimensionless fracture conductivity is less than 0.1 if you will use in calculation of permeability
from hydrodynamic studies, which indicates a low efficiency of the fracturing. However, if you would
like to use petrophysical dependence "porosity vs permeability", the dimensionless conductivity will
be calculated about 1. There is need revision of the dimensionless conductivity (FCD) for the cyclite
of alluvial flat part due to large range of uncertainty in permeability.
First stage of pilot works
The first stage involved testing the hydraulic fracturing technology in directional wells. Several zones with
different geological conditions and facies zones have been identified in order to determine the possible
volume of replication of this technology (Pic. 1): two candidate wells in zones with a natural restricted zone
(clay jumper between oil and water-saturated sublayers); two candidate wells without a clay jumper, with
multiple sublayering of the reservoir (water-contact reserves); one well candidate with a targeted fracture
break through water-oil contact to estimate the starting value and dynamics of the water cut; and one
candidate well for the analysis of technical possibility multistage fracturing.
SPE-187682-MS
3
Picture 1—Geological facies and candidate wells location
General risks and uncertainties
The main factors that influence on the possibility of fracturing are small depth and geographical position of
the Vostochno-Messoyakhskoye field, which allow the presence of a strike-slip fault regime (lateral strain
exceeds vertical). The stress state at depths up to 1 km subject to strong influence of tectonics, in our case
absolute vertical depth is 800m. As the source of the stress usually distinguish the forces that motivate
the movement of lithospheric plates, fault structure, flexure stress caused by external loads (e.g. mountain
ridges). Data analysis and 1D geomechanical model of the wellbore has shown that there are the following
uncertainties: stress regime (normal or stike-slip), the minimal horizontal stress (no calibration points),
lateral uncertainty of the orientation and magnitude of stresses due to the presence of faults, the influence
of the plastic properties of rock. All this involves risks to the geometry of the fracture (the uncertainty on
the height of the fracture and its orientation). In addition, in strike-slip regime it is possible formation of
complex fractures: a planar, horizontal or T-shape. This form of fracturing is extremely undesirable, since
in this case there will be proppant bridging and early packing of the proppant in the near wellbore zone.
Commercially available hydraulic fracturing simulators do not allow to evaluate this effect.
Handling uncertainties 3D MEM was building to account for the potential availability of normal and
strike-slip regimes. From the simulation results, the most probable scenario showed the evolution of the
classic vertical fractures.
In order to evaluate fracture geometry and handling uncertainties for further replication, in pilot works
case hole logging was performed, SFM with cross-dipole acoustic, neutron logging, coupled with the
marked proppant. In all jobs autonomous downhole pressure and temperature gauge were useds for the most
correct estimation of the fracture geometry and collbration of actual and model values of pressures
Also, this complex of logging and direct measurements of bottom hole pressure during fracturing allow
us to remove the uncertainty on the second negative factor - high probability of fracture growth inwatersaturated and gas-saturated zaones of the reservoir due to the lack of fracture barriers. The results of well
flow back are qualitative and quantitative indicator of the degree of fracture geometry control.
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SPE-187682-MS
The third risk factor is the combination of low reservoir temperatures with the presence in the
mineralogical composition of the reservoir montmorillonite clays affected to swelling. Low reservoir
temperature be an issue for gel destruction and leads to formation damage. For removing this risk has been
planned and realised program of laboratory tests consisting of tests of different frac fluid compositions on
core plugs. In framework of this program series of sequential laboratory filtration tests were performed
with step-by-step change of all components, since the basis fluid (fresh or brackish reservoir water) and
ending with the selection of complex breakers (standard oxidizing agents to enzyme breakers). The result
was the optimal composition based on fresh water with a combination of low-temperature oxidative and
enzyme breakers.
Another factor complicating the successful hydraulic fracturing is a weak consolidation of sandstone.
Basic wells completion is liners with premium filters due to the high removal of the suspended mechanical
particles. The experience of well operations is show absence of correlation of the SSC (suspended solids
concentration) with the filter type, mesh size, bottom hole pressure and geological-facial conditions. In this
regard, it was decided in pilot operations in directional wells not to apply any methods of consolidating
proppant for specific assessment of SSC and porppant backflow. When further jobs in horizontal wells
planned use of specialized copmletion, which combine frac sleeves and mesh filteres in order to minimize
the SSC and proppant flowback.
To prepare quality designs of hydraulic fracturing for a number of wells it was observed the lack of
available logging data - density and acoustic logs, which are necessary for the correct evaluation of the
elastic-mechanical properties of reservoir. To minimize the risk of inaccurate fracture geometry design cross
corellations based on neural network was performed in order to restore density and acoustic log from the
other logs.
Phasing and results of pilot works
The implementation process of hydraulic fracturing in directional wells have been performed with stepby-step increasing of the aggressiveness of treatments from well to well. This approach ensured failsafe
operations in pilot works (the absence of technological complications) and allow us to estimate the reserve
potential of aggressiveness of the design of the fracturing treatment. The main task was failsafe pass from
the classic fracturing technology to TSO that allows you to create the widest possible fractures at a low
altitude and to maximize the parameter of the dimensionless conductivity (FCD). In particular, the maximum
concentration of proppant on the first operations were 900kg/m3, for the last 1400 kg/m3, fixed width is
increased from 3.3 mm to 9.4 mm, the proppant size16/20 with up to 12/18.
Implemented complex research allows to confirm the hypothesis about the formation of the classic
vertical fractures, example of one of well provides a comparison of the different methods of predicting the
fracture geometry (Pic.2).
SPE-187682-MS
5
Picture 2—Comparison of different methods of estimating fracture height
As can be seen, the fracture height calibrated on real BHP and geomechanical model concides with the
fracture height estimated from SFM (used 2 deifferent acoustic tools, which show similar results). A similar
result shows the method of mapping fracture based on the marked proppant (marker – gadolinium, the entire
volume of the injected proppant - marked) and neutron logging before and after fracturing. This method is
allow to estimate the height of highest propped width interval.
The results of wells operations confirmed calibrated model design of fracture and performed estimation
of fracture geometry. Oil, gas and water rates of wells indirectly indicates the fracture geometry and fracture
growth in water and gas zones.
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SPE-187682-MS
Conclusions
Based on the results of testing and testing of exploratory wells with hydraulic fracturing:
•
•
•
•
•
•
Approve technological possibility of hydraulic fracturing on unconsolidated and high-permeability
heavy oil reservoir
Approve creating traditional vertical fracture by geophysical methods and by the results of
production
Value of fracture height by different methods of mapping fracture geometry are semi-comparable,
which makes it possible to estimate the averaged value of each parameter
Performed complex of geophysics logging allows to estimate in technological efficiency of
hydraulic fracturing
Performed complex of laboratory studies of various chemical compound hydraulic fracturing fluids
on the core material made it possible to select the optimal compound with minimal negative impact
on the formation
Step-by-step method increase of the aggressiveness of the treatment designs allowed the accidentfree implementation of pilot works and estimate of possible aggressiveness to tip screen out (TSO).
In the continuation of described work, it is planned to implement the second stage of pilot hydraulic
fracturing works by testing of specialized completion systems with the combination of frac sleeves and the
filter part on the design horizontal wells of production drilling.
References
[1] Economides, M. J., Oligney, R.E. and Valko, P.P.: Unified Fracture Design: From Theory to
Practice. – Moscow – Izhevsk: The Institute of computer knowledges, 2007. – 236.
[2] Mark L. Wedman, Keith W. Lynch and Jim W. Spearman. Hydraulic Fracturing for Sand Control
in Unconsolidated Heavy-Oil Reservoirs. SPE, BP Exploration (Alaska) Inc, p. 12, May. 1999.
[3] J. Italo Bahamon, C. Garcia, J. Manuel Ulloa, and J. Leal. Successful Implementation of
Hydraulic Fracturing Techniques in High Permeability Heavy Oil Wells in the Llanos BasinColombia. SPE, Ecopetrol, Weatherford, p. 13, Nov. 2015
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