Page 396 - Fundamentals of Gas Shale Reservoirs

376 GAS SHALE CHALLENGES OVER THE ASSET LIFE CYCLE

effective method of determining production rates coming of necessary equipment. Chemical automation systems
from individual perforated stages. Some operators have run can be used, especially for remote locations, widespread
production‐logging tools (PLT) in horizontal wells to mon- operations, and in low‐winter temperature operations.
itor production (Heddleston, 2009). However, the question
begs as to whether any significant remedial work might 17.6.5 Protecting the Environment
be attempted (or be economically justified) aside from a
cleanout, chemical treatment, or possible refrac. One other Protection of the environment should be included in every
method of monitoring production from individual stages has phase of the life cycle; however, it is particularly critical dur-
been employed, that is, DTS. A few wells have been equipped ing the production phase when hydrocarbons and water are
with DTS, but the fiber‐optic cable and equipment must be brought to the surface.
installed as part of the original completion and the cost is
difficult to justify based on as yet unproven benefit.
17.7 REJUVENATION PHASE DISCUSSION
17.6.3 Manage the Water Cycle—Recommended It is the opinion of this author that the most significant
Practices opportunity to accomplish rejuvenation lies with refracs. As
Most shale gas wells do not produce any significant has been discussed, unconventional wells decline rapidly
amounts of water, and the water produced by tight gas reaching low unacceptable rates after only a few years of
wells is handled with deliquification techniques—plunger production. It has not been proven that any form of produc-
lift, foam sticks/continuous foam injection, gas lift, beam tion management or enhancement has been successful in
lift pumps, and jet pumps. Water that is of concern with arresting the rapid decline or restoring original production
shale wells is frac flowback water. Although not all of the rates. In his database of 100 published studies on refracs,
frac water comes back (typically about 30%), the amount Vincent (2010) attributed re‐frac success to a number of
that does brings with it formation salts, scale, and some- mechanisms as listed in the following:
times low‐level radiation (NORM). Frac flowback water
must be treated, whether it is to be reused or disposed. • Enlarged fracture geometry, enhancing reservoir contact
With the water situation in many parts of the country and • More thorough lateral coverage in horizontal wells or
the world, reuse is strongly recommended. Service com- initiation of more transverse fractures
panies provide water‐treating services for flowback and • Increased fracture conductivity compared to initial frac
produced water. Currently, the most popular and effective • Restoration of fracture conductivity loss due to
equipment uses electrocoagulation technology to remove embedment, cyclic stress, proppant degradation,
suspended solids and heavy metals from flowback and pro- gel damage, scale, asphaltene precipitation, fines
duced water. Freshwater is not required for fracturing plugging, and so on
wells. Formation brine water and seawater are other alter- • Increased conductivity in previously unpropped or
natives. Additional frac additive chemicals are required inadequately propped portions of fracture
due to salt content of these waters. There is more to • Improved production profile in well, preferentially
managing the water cycle than treating and or disposal. stimulating lower permeability intervals (reservoir
Water sourcing for both drilling and fracturing has become management)
significant. In the Eagle Ford, water is being sourced from
shallow salt water formations and being lifted from wells • Use of more suitable fracture fluid
using large‐volume electric submersible pumps (ESPs). • Reenergize or reinflate natural fractures
On the surface, produced and treated water must be han- • Reorientation due to stress field alterations, leading to
dled and transported to central processing/treating facil- contact of “new” rock
ities or removed for disposal. This requires piping and
surface transfer pumps. Production rates from refracs have matched, or sometimes
exceeded those from the original frac. Examples in the lit-
erature show increased production rates, especially in the
17.6.4 Preventing Corrosion, Scaling, and Bacterial Barnett, where wells were restimulated with slickwater fracs
Contamination in Wells and Facilities
versus the original gel fracs.
Corrosion, scaling, and bacterial contamination in wells and Redevelopment of a shale or tight gas field will more than
facilities is handled much the same way as in traditional likely involve infill drilling to accomplish downspacing.
oil and gas fields. Components of a production chemical This has already been seen in the Pinedale and Piceance tight
program include the chemical treatment program, moni- gas plays, where original well spacing of 160 acres has
toring of program effectiveness, and design and installation now gone down to 5–10 acres. Redevelopment should be