CONTROLLING SAND PRODUCTION

Based on workshops sponsored by PTTC's West Coast Region on Nov. 18 & 19, 1999 in Long Beach and Bakersfield, California

BOTTOM LINE

Cost effective solutions exist for controlling sand production, ranging from conventional gravel packs to High Rate Water Packs to Frac Packs to a novel steam sand consolidation completion technique. But operators must know when to apply the different solutions. Controlling proppant flowback after fracturing is also critical.

PROBLEM ADDRESSED

In certain areas (like much of California), sand production is a major operational problem. In some circumstances, it is most economical for operators to just live with the problem. Even then operators must deal with erosion problems, as well as sand fill whenever production is interrupted, and eventual wellbore collapse. Frequently though, sand control treatments are required. Like with most problems, there are several technology optionsopen hole or cased, conventional gravel pack, prepacked screens or liners, Frac Packs or High Water Rate Sand Packs, etc. This workshop provides a comprehensive look at sand control and the knowledge required to choose the optimum solution.

KEY WORDS:

Frac Pack, Gravel packing, High Rate Water Pack, Sand control, Sand consolidation

SPEAKERS

Successful Sand Control
Derry Sparlin, International Completion Consultants Inc.

Gravel Packing Practices
Mike Gleason, Baker Oil Tools

Sand Consolidation with Steam Injection
Scott Hara, Tidelands Oil Production Company

Controlling Frac Sand Production
Porter Underwood, Halliburton

Sand Control Practices
Mary Edwards, B. J. Services

TECHNOLOGY OVERVIEW

Knowing the nature of the sand, which is best learned by examining cores, is an essential first step. Monitoring sand concentration in produced fluids can help identify "quicksands" (high and relatively constant sand concentration), "partially consolidated" sands (concentration fluctuates widely), and "friable" sands (taper off to nearly zero after a well has been on production for awhile).

Because of the nature of oil-field sands, slotted liners or screens by themselves (without gravel) are rarely effective in controlling sand production. For a successful gravel pack, it is necessary to: (1) size the gravel to stop movement of formation sand, (2) place gravel in a tight pack that has a radius as large as possible, and (3) maximize productivity while minimizing formation damage. Open hole gravel packing is common in vertical wells because it is easiest and usually less expensive than other options, although hole stability, screen plugging, and thief zones can be a problem. This method is generally limited to a bottom interval in multiple zone completions.

The size of gravel pack sand that should be used depends on size of the formation sand. This is determined from sieve analysis, preferably from core samples (bailed samples tend to be large, produced samples tend to be small). Gravel pack sand is normally sized to achieve a median grain size ratio (gravel/formation) of 6, multiplying the median formation sand size by 4 and 8 to get a gravel size range. There is a trend towards using larger sizes. Screen or slotted liner openings should be no larger than 70% of the smallest gravel pack sand diameter. Prepacked screens and liners must be appropriately sized.

Three basic tools are used in gravel packing operations: (1) packer/crossover tool assembly, (2) over-thetop tool assembly, and (3), in some cases, port collars. Some are completion tools that remain in the well after the gravel pack is complete. On the other hand, service tools are used while placing the gravel pack but then are removed.

Sand is introduced using a Pot Machine or specialized gravel infuser. Although more costly, the Infuser system offers several advantages, including more precise mixing, lower completion fluid volumes, and reduced rig time. Either completion fluids (produced water or prepared brines) or viscous fluids can be used as carrier fluids. Non-viscous completion fluids are more economical, but higher volumes are required and filtration requirements are more critical with the higher leakoff. Experience indicates that cleanliness is critical to job success. Cleanliness covers the entire system— casing, tubing, tanks, lines, completion fluid, equipment and gravel.

There are three basic gravel pack processes: (1) High Rate Water Pack, (2) Frac Pack, and (3) Horizontal Gravel Pack. Frac Packs are a combination of a fracture treatment and an annular gravel pack. A successful Frac Pack must not only stop sand movement, but must create a wide fracture that is held open by a high permeability proppant extending through the nearwellbore zone, importantly not making contact with nearby zones that contain unwanted fluids. A High Rate Water Pack (HRWP), which pumps water and sand at high rates creating short fractures, maximizes gravel placement in the perforations. Treating pressures may or may not exceed fracture pressure.

HRWPs are typically used where the completion is near water or gas contacts and there is a shallow radius of near wellbore damage combined with relatively uniform sand quality and permeability. In contrast, Frac Packs, which create much longer fractures, are used where sands are laminated, where fines migration potential exists, or where deep formation damage is known or suspected.

In high angle and horizontal wellbores, any formation that will not collapse while drilling a long horizontal, should be strong enough to not produce sand. This is also true with removing the drilling equipment and running a liner/screen. Sand problems occur with excess water production, too much pressure reduction, or with high drawdown (high production from short intervals). Just as with vertical wells, slotted liners or wire wrapped screens should be used in conjunction with gravel packing. Ungelled brine is typically used. Special prepacked screens and downhole filters, which are sometimes used in horizontal wells, can be susceptible to plugging and collapse. Before installing prepacked screens or liners, it is important to apply a thin coat of acid soluble materials, waxes, or wax-polymer blend to them to reduce screen/liner plugging.

When designing horizontal gravel packs, it is important to define the allowable pump operating ranges. Pump rate must be high enough to exceed the rate of fluid loss and to push dunes of gravel to the end of the screen. The ALLPACK TM system, an alternative approach which eliminates the need for a prepacked screen, is gaining acceptance. This system uses small diameter tubes strapped along the outside of the screen that allow gravel to be pumped at high velocities. A controlled viscosity (50 to 100 cp) fluid is used to suspend gravel and aid its transport.

Controlling Frac Sand Production.
Control of proppant flowback is important to maintain connection between the fracture and wellbore, maintain fracture conductivity, maintain formation stresses, and prevent wellbore fill and pumping problems. The nature of the completion itself (perforations, liners/screens, etc.) influences proppant flowback, while stability is a strong function of flow rate, particle size, frac width, and closure stress. The flowback initiation rate decreases as the closure stress increases and as the fracture widens. Conversely, it increases with proppant size.

Proppant control measures should be employed both during and after the fracturing process. During fracturing, measures can include inner liners/screens, fiber and bridging techniques, resin coated proppants, or surface modifier agents. After fracturing, measures can include inner liners/screens, in situ resins with external catalyst, or sand "squeeze" with resin or surface modifying agent. Applying sand control measures during fracturing is much more cost effective than remedying problems after the fact.

Sand Consolidation with Steam Injection.
Like many California fields, sand production is a prevalent problem in thermal operations in Wilmington Field's unconsolidated turbidite sands. Conventional completions are open hole, gravel packed with a slotted liner. Beginning as early as 1990, Tidelands Oil Production Company began experimenting with alkaline hot water/steam sand consolidation. For this novel technique, wells are cased and cemented, then completed with limited entry perforations, and injected with steam of 60-80% quality. This process provides a highly alkaline (pH= 10-12) liquid phase and temperatures to 300 o C to geochemically create cements by interacting with the dirty sand. Empirical experience indicates that minimum steam volume is 750 barrels of cold water equivalent per perforation.

The hot alkaline liquid phase causes sandstone dissolution, preferentially acting on sand grains with high specific area such as clays, rock fragments, and micas. The technique creates secondary porosity resulting in increased permeability. As the injected fluids exit the perforations and cool, various precipitates drop out at different temperatures. High temperature precipitates bond the sand grains around the perforations, controlling sand movement. Lower temperature precipitates, which can cause adverse effects, are driven away from the wellbore by injected fluids, especially the steam vapor phase.

The sand consolidation technique has been applied in 12 horizontal wells and 22 vertical wells with over 90% of the wells capable of production or injection after two years. Wells completed with this technique have equivalent or higher productivity and injectivity than conventional open hole gravel packs, and costs are lower due to substantial savings in well drilling and completion operations. Production and injection profiles are improved because of the limited entry approach. Additionally, since the created synthetic cements resist hydrochloric acid, wells can be acidized to remove scales and other formation damage.

CONNECTIONS:

Mary Edwards
B. J. Services
11211 FM 2920 West,
Tomball, TX 77375
Phone 281-357-2840, Fax 281-357-2840, E-mail medwards@bjservices.com

Mike Gleason
Baker Oil Tools
1404 Fleet Ave., Ventura, CA 93003
Phone 805-644-8159, Fax 805-644-8771, E-mail mikegleason@bakeroiltools.com

Scott Hara
Tidelands Oil Production Company
301 East Ocean Boulevard, Suite 300,
P. O. Box 1330 Long Beach, CA 90801
Phone 562-495-9351, Fax 562-495-1950, E-mail tidelands@95net.com

Derry Sparlin
International Completion Consultants Inc.
One (ICCS) Cornerstone Plaza, 3845 FM 1960 West #335
Houston, TX 77068
Phone 281-444-1014, Fax 281-444-0615, E-mail icci@ix.netcom.com

Porter Underwood
Halliburton
5500 Ming Ave., Suite 365, Bakersfield, CA 93309
Phone 661-837-2971, Fax 661-837-0201, E-mail Porter. Underwood@Halliburton.com

For information on PTTC’s West Coast Region and its activities contact:
Iraj Ershaghi, Director, Petroleum Engineering Program, HEDCO-316
University of Southern California, Los Angeles, CA 90089-1211
Phone 213-740-8076, Fax 213-740-7982, E-mail ershaghi@archie.usc.edu

Disclaimer: No specific application of products or services is endorsed by PTTC. Reasonable steps are taken to ensure the reliability of sources for information that PTTC disseminates; individuals and institutions are solely responsible for the consequences of its use.

The not-for-profit Petroleum Technology Transfer Council is funded primarily by the US Department of Energy’s Office of Fossil Energy, with additional funding from universities, state geological surveys, several state governments, and industry donations.

Petroleum Technology Transfer Council, 2916 West T. C. Jester, Suite 103, Houston, TX 77018
Toll-free 1-888-THE-PTTC; Fax 713-688-0935; E-mail hq@pttc.org; web www.pttc.org