Oil&Gas Eurasia July-August 2016

R&D
Optimisation of Hydraulic Fracture
Spacing for Gas-condensate
Reservoirs
Benson Lamidi Abdul-Latif, Saint Petersburg Mining University, Saint
Petersburg, Russian Federation; Oppong Riverson, Gubkin Russian State Oil
and Gas University, Moscow, Russian Federation
Owing to the gradual depletion of conventional hydrocarbon
reservoirs there is a great desire of oil producing
countries to sought new hydrocarbon sources for
economic, security and political reasons. Shale gas, tight gas,
coldbed methane (CBM) and gas-condensate reservoirs have
all become very prominent.
The advent of horizontal well technology and the
applications of hydraulic fracturing in horizontal gascondensate
wells have played a vital role in shale gas
and condensate reservoir development. The primary
goal of hydraulic fracturing in horizontal gas wells is
to generate a highly conductive flow path from the
reservoir through the created hydraulic fracturesinto
the wellbore in order to economically and technically
increase gas well productivity index. The primary variables
that control the productivity of a fractured well
are the fracture length, the dimensionless fracture conductivity
and the fracture density (fracture spacing).
In moderate and high permeability wells, insufficient
fracture conductivity is a limiting factor in the production
potential of the well, whereas the limiting factor
in tight gas reservoirs is usually the effective fracture
half-length. Fracture density on the other hand plays a
pivotal role in optimizing gas well deliverability in both
tight and lean gas reservoirs.
Even with the advent of horizontal well technology,
technological challenges such as condensate banking and
bottomhole pressure depletion in gas reservoirs makes
gas condensate reservoirs one of the most challenging
natural gas reservoirs. Condensate banking is still a major
problem challenging the exploitation of gas condensate
and shale gas reservoirs. Formation damage in gascondensate
reservoirs are usually caused by condensate
buildup around fractures and wellbore hence reducing
the relative permeability to gas and thereby decreases the
gas well deliverability.
In a gas condensate reservoir, poor fracture density
(spacing) and design might lead to lower gas production
with a higher economic cost. Due to the fact that pressure
gradient are usually created normal to a fracture, liquid
condensates are usually formed within a fracture which is
also one of the major factors affecting relative permeability
to gas in the reservoir. Such permeability reductions
depend on phase behavior of the fluids and penetration
of liquid condensate, which in turn, depends on the pressure
drawdown imposed on the well. This effect causes
an apparent damage that affects the performance of all
hydraulic fractures in gas-condensate wells.
In this paper, optimization techniques and methods
are used to determine optimal fracture design and density
(spacing) using hydraulic fracturing and horizontal well
technology in gas condensate reservoirs, thereby reducing
fracture interference, unnecessary economic cost
and minimizing fracture face damages. Using simulation
methods, fracture spacing was optimized as functions of
well flow rate, net present values (NPV), gas prices and
gas cumulative production. Also, the effect of parameters
such as permeability, pore size on phase behavior and
non-Darcy flow on the production of gas-condensate reservoir
is presented in this paper.
Simulations results showed that higher gas prices
allow for tighter fracture spacing so as to accelerate gas
recovery rate and hence increases the well NPV.
Also, sensitivity tools were used to identify factors
affecting fracture spacing in gas condensate reservoirs.
This paper also outlines optimization studies on
fracture geometry (fracture length in gas-condensate
reservoirs) andfracture spacing in which both analytical
and numerical tools were used for several developmental
scenarios in the gas-condensate reservoir environment.
The design strategy for optimizing the fracture treatment
once it has been decided to fracture must evidently
include economic considerations. We will not carry the
procedure out to the extent that the return on investment
is calculated, since all of the factors including interest
rates, gas prices, taxes, treatment costs, etc., will vary,
making obsolete any results based on assumed values.
The technical problem of optimizing fracture design and
density can, however, be separated from the economic
aspects if the procedure recommended here is followed.
Introduction
There are several challenges in a gas-condensate reservoir
using horizontal and hydraulic fracturing technology.
Fracture performance is always likely to be affected
greatly by the presence of liquid condensate, which normally
leads to fracture face damages. For unconventional
reservoirs, gas-condensate become more exciting as the
condensate banking effect is severer due to high-pressure
drawdown from matrix to hydraulic fracture (Ismail et al,
2015). Whilst most condensate banking in conventional
reservoirs can be mitigated by miscible and immiscible
48 Oil&GasEURASIA