Chapter3批评之后>超凡的意思
Tight Gas Rervoir Simulation
Analytical and numerical simulation studies are performed to have a qualitative understanding of damage mechanisms associated with production from non-frac-tured and hydraulically fractured tight gas rervoirs;and evaluate its potential impact on well productivity.
In building tight gas rervoirs simulation model,it is important to u a consistent t offield data in order to get meaningful simulation outputs.Bad on a West Australian tight gasfield data,the simulation models are built at rervoir scale and core scale.In this chapter,rervoir simulation studies for different types of well and tight rervoirs are prented.
3.1Effect of Damage Mechanisms on Well Productivity Rervoir simulation is ud to understand how damage mechanisms are con-trolled by the well and rervoir parameters such as rervoir permeability,per-meability of the damaged zone,radius of the damaged zone,drillingfluid type, capillary pressure and relative permeability curves.
In this ction,the effects of different parameters on damage and skin factor are studied using the rer
voir simulation models.To evaluate the damage effects,the termflow efficiency(FE)is ud in some of the cas,which is defined as the ratio of the pressure drop across the model in the ca of zero skin virgin homogeneous rock;to the pressure drop in the ca of perforated and/or damaged rock(FE equals to1in the ca that there is no damage introduced to a non-perforated model).
3.1.1Damaged Zone Permeability and Radius
The simulation model is run for conventional and tight cores,with damaged zone permeability of K d and damaged zone radius of r d.The model results are shown in
21 N.Bahrami,Evaluating Factors Controlling Damage and Productivity in Tight Gas Rervoirs,Springer Thes,DOI:10.1007/978-3-319-02481-3_3,
ÓSpringer International Publishing Switzerland2013
Fig.3.1.According to the results,the effect of damaged zone permeability and damaged zone radius on flow efficiency is more significant in tight gas rervoirs compared with conventional cores,indicating the importance of damage control in tight gas rervoirs.
3.1.2Pha Trapping Damage Caud by Water Invasion
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The effect of water invasion in the rervoir model is evaluated by injecting water at the well location,followed by gas production.The water saturation in the rervoir model at initial conditions (top view)is shown in Fig.3.2(S wi =0.6).First,water is injected at the well location,which increas water saturation around the wellbore.Water saturation at the end of the injection period is shown
in Fig.3.1Invaded zone
parameters and the effect
on flow efficiency X Y 100 ft 100
ft
S w
Fig.3.2Water saturation
in the model before water
invasion
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3Tight Gas Rervoir Simulation王莽篡汉多少年
Fig.3.3(equivalent radius of water invaded zone:9ft).Afterwards,the model is put on gas production to clean-up the invading water,and reduce water saturation around the wellbore.Water saturation at the end of the gas production period is shown in Fig.3.4(equivalent radius of water invaded zone:12ft).The results indicate during the gas production pha,not only water from the near wellbor
e was not cleaned up by gas production,water invasion was continued into the rervoir due to the strong capillary pressure suction effects,and damaged zone radius (water invaded radius)incread with passage of time.S w
X
Y 100 ft 100
ft
Fig.3.3Water saturation
in the model at the end of
water injection period X Y 100 ft 100
ft
S w
Fig.3.4Water saturation in
the model at the end of gas
production period
3.1Effect of Damage Mechanisms on Well Productivity
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3.1.3Effect of Pha-Trap Damage on Skin Factor
The rervoir model is also run to understand the effect of pha trapping damage on skin factor for four different cas.Ca A considers no leak-off of liquid into formation (no damage).Cas B,C and D,consider,respectively approximately 215,770and 1400barrels of water leaks off into the formation.In each run,the water leak-off is followed by gas production during clean-up.
In each of the models after the liquid leak-off,the well is put on gas production followed by a pressure build-up test.The pressure transient data are generated to calculate the skin factor caud by pha trapping.The cumulative injected volume of water during leak-off (W i )and the simulated results for cumulative produced water (W p )during clean-up and gas production are integrated with welltest results as shown in Fig.3.5.In the ca of no liquid leak-off into the tight formation (ca
A),the water blocking skin is zero.In the ca of significant water leak-off into the formation,skin is found to be positive.The results highlight the fact that pha trap related damage due to water leak-off into the tight gas rervoir caus positive skin factor,and significant reduction in gas production rate and gas recovery.
3.1.4Overbalanced and Underbalanced Drilling
The model is run at core scale,to understand the effect of wellbore pressure on water invasion during overbalanced,balanced and underbalanced drilling.The model is run for the following cas.
•500psia overbalanced pressure resulted in 0.500liquid invasion into
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Fig.3.5Effect of pha trap damage on skin factor
243Tight Gas Rervoir Simulation
•Balanced pressure conditions resulted in 0.400liquid invasion into matrix •400psia underbalanced resulted in 0.300liquid invasion into matrix
•1000psia underbalanced resulted in 0.300liquid invasion into matrix.
From this simulation results as shown in Fig.3.6,it is obvious that the wellbore liquid invades deeper in overbalanced conditions.However for underbalanced conditions,although the wellbore pressure is less than the rervoir pressure,water still invades the matrix rock due to the strong capillary suction and caus an increa in water saturation around the wellbore.Thus,damage caud by water blocking might still be significant even in the ca of underbalanced drilling in tight formations,owing to the ability of high and negative capillary pressure (water suction)to compensate for relatively low mud pressure in the common ca where the tight gas formation is strongly water
wet.Fig.3.6Effect of wellbore pressure during drilling on pha trap damage
3.1Effect of Damage Mechanisms on Well Productivity 25
