Reservoir Engineering Aspects of Gas Well Deliquification

Break-out Session

Efrén MuñozConocoPhillips

Feb/2010

Question 1:How to deal with liquid loaded wells

in order to estimate reserves?Production optimization efforts will pay off when we have a better handle of cumulative production and remaining reserves. In this case Reservoir Engineers must be familiar with liquid loading effects to avoid very pessimistic or very optimistic forecast estimations. Integrated production modeling was proposed as a good alternative as the nodal analysis model will take care of the stability of the well while producing. A word of caution though, this is valid if a “fully transient” model is used to generate the IPR model, as Petroleum Experts claim to do it in MBal, not in Prosper. This is definitely a topic for the RE’s to come into the picture and decide how to do it.

Let’s review the completion and logs, single layer (0 < b < 0.5)

Historical production, showing a well capable to produce 200 mcfd

“4 in 1 Plot” analysis

Slope=-1 n=0.75,

b=0.33n=0.75,

b=0.33

Slope=-1, depletion

After correcting “b=0.33” (single layer), rate uplift= 175 mcfd,

incremental reserves= 320 MMcf

Incremental reserves with starting rate= 185 mcfd

What is your average rate?

Noisy data, sensitivity analysis

P10, P50, P90

Assuming that surface pressure remains constant, the starting rate can affect

dramatically RR and economicsRemaining Reserves (based on Forecast)

0

0.05

0.1

0.15

0.2

0.25

0.3

1 11 21 31 41 51 61 71 81 91 101

111

121

131

141

151

161

171

181

Time (months)

Cum

Gas

(Bcf

)

CumP10CumP90CumP50

Question 2:Multi-layer, do we understand the effects on decline curve

analysis?No, the general consensus is that we know this is an issue, but we have to live with it, the issue becomes more critical when there is differential depletion among the producing layers and then we have to re-evaluate “completion” techniques, in other words produce zones separately, and avoid commingled production while pressures are not equalized.

Completion (multi-layer)

Sensitivity to “b”, considering b=0.35, 0.4 and 0.54

Effect of “b” factor on RR, in this specific case b=0.54, multi-layer (0.5<b<1.0)

Remaining Reserves (based on Forecast)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 10 20 30 40 50 60 70 80 90 100

110

120

130

140

150

160

170

180

190

200

210

220

230

240

Time (months)

Cum

Gas

(Bcf

)

B_04B_03 B_054

Question 3:What is the real effect of a water

column on the permeability of the near wellbore area?

Open topic, the accepted explanation in this session is that as the condensate blockage in a gas well, water also creates a liquid bank close by the sand face that works as an additional formation damage. Those fluids have to be produced to lower the water saturation and hence relative permeability to water is reduced, in that way gas relative permeability increases and production is re-stored eventually. Is not a rapid process, it can take weeks or months depending on the k.h of the specific interval. One recommendation is to always keep the well unloaded, it may be as simple as injecting foam continuously, or if necessary helping with artificial lift.

Open to discussion

Additional topics:– Water measurement: this is still a big issue, we are still

measuring water at manifold or battery level, then we back allocate water production to each well individually, which is not accurate. Is was agreed that the services companies should look for cheaper ways to measure water at wellhead level.

– Monitoring fluid levels: this was another idea, the use of wellhead pressure gauges (i.e. Spidr, Echometer, RDS, etc) to monitor fluid level movements with time. Sounds good, is a cheap alternative to monitor how the liquid level is moving and also helps to refine artificial lift designs.

Open to discussion (cont)

Additional topics (cont):– Liquid loading prediction: somehow all

companies are monitoring liquid loading with Scada systems or similar technologies, however, is not common to predict this effect, this is another topic to send as feedback to the services companies, may be more for the software companies (i.e. automation?) to have a better use of the available commercial software that is fed by Scada data.

Attendees:Efren Munoz (facilitator)James Dickerson Jason FranklinJimmy CostalezStefan BelfroidMark GrenfellSenn PetersenJesse GraciaCarter ClemensJason JosephJeff DavisGeoffrey Steiner