Summary
This case study outlines the techniques used to model the Williams
Production Rocky Mountain Co. Grand Valley gas-gathering system in the Piceance
basin. The results of the modeling exemplify how a nodal-analysis model
can become an invaluable tool for optimizing the performance of gas-gathering
systems and planning future system expansion.
Field production in the Grand Valley gathering system varies minute by
minute, creating a dynamic system that is difficult to model with standard
practice. By use of an innovative statistical method to handle the scale
and complexity of the system, the model has simulated the true flowing
conditions of the system over the last 5 years consistently and
accurately. The model has been used to successfully locate and quantify
substantial static and frictional pressure losses. As the field develops,
proposed drilling programs are added to forecast the impact of the new wells on
the system. Various pipeline and compressor-expansion scenarios are
tested to determine the most effective locations and cost-viable options.
Recommendations from the model have been implemented successfully and have
played an integral role in the expansion of the gathering system. The
model has been used to identify exact locations of pressure losses, help plan
for incremental drilling volumes, and quantify the additional costs incurred
from third-party gas entering the system.
This paper explains how a model can assist in the successful development of
a large-scale, high-volume, and dynamic gas-gathering system. Details of
the modeling procedure and highlights of the innovations implemented to meet
the challenging operating conditions and aggressive development of this field
are presented.
Introduction
The Piceance basin in western Colorado is one of the most rapidly developing
areas of unconventional gas production in the United States. The gas is
produced from the Mesaverde group, which consists of sands interbedded with
shale. The main target formation is the tight, discontinuous, lenticular
sands of the Williams Fork formation. The net pay of the formation is
thick—generally hundreds of feet deep—but the low permeability of the formation
substantially limits flow potential. There are also several wells producing
from the Wasatch and Rulison formations. The production from these shallower
zones accounts for approximately 1% of the total field production.
Development of the fields has been historically slow because of marginally
economic flow rates. Recent high gas prices and increased consumer demand
have accelerated basin development in the past few years, and infill and
step-out drilling have increased the assigned reserves of these fields
significantly.
While the reserves of the basin are extensive, the drainage area of a single
well is quite small, limiting the recoverable reserves on a per-well basis to
approximately 1.0 to 1.2 Bcf. A large number of wells is required to
deplete the resource within an economic time frame. Throughout the
history of the fields, the interwell spacing has been successively decreased
from 80 to 20 acres. At the current spacing of 20 acres, the production
history has shown minimal interference between the wells. A pilot project
currently is being conducted to determine the feasibility of decreasing the
interwell spacing to 10 acres.
Over the last 5 years, in the midst of rapid expansion, Williams has used a
nodal-analysis model to plan the development of their gas-gathering system
successfully. From 2000 to 2005, the model was updated on a yearly
basis. Because of the continuous system expansions and upgrades, Williams
is now updating the model on a monthly basis.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
6 March 2006
- Revised manuscript received:
18 July 2006
- Manuscript approved:
20 July 2006
- Version of record:
20 September 2006
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