March 2002 Supplement  Case Study

Unique chemical removes paraffin damage, stimulates production

Rick Stewart, MOCO Operating Co., Lafayette, La.; and Donald R. Ford,* Chem-Tec LLC, Lake Charles, La.

Bottom line. MOCO Operating Co. treated two Upper Wilcox wells in Southeast Louisiana with a paraffin-asphaltene chemical that works via unique mechanisms. The treatments, which cost about $20,000 each, more than tripled production (from 3 to 8 bopd to the mid 20s), paying out in less than three months. Some six months later, production was still holding steady at more than double pre-treatment rates. MOCO now considers this chemical part of its routine treating program.

Problem addressed. In areas with highly paraffinic crudes, such as Southeast Louisiana, paraffin blockages can significantly reduce production. Conventional paraffin treatments, such as hot oil or water, solvents, dispersants and wax crystal modifiers, have their place, but there are limitations. Solutions involving more benign chemicals that have quick and longer-lasting results are needed.

Field background. South Bearhead Creek field in Beauregard Parish in Southeast Louisiana was originally developed in the late 1940s and early 1950s. Further exploration has continued through 2000. Production primarily comes from the Upper and Lower Wilcox. The Wilcox in Beauregard Parish is, put simply, tight. Zones are typically hydraulically fractured. Wells exhibit early response, then decline to lower and sometimes marginal rates. Paraffin problems can be severe.

The two completions referenced in this case study had been fractured and had become marginal wells producing less than 10 bopd. Both had a history of paraffin problems. MOCO chose these two wells for treatment because they represented two different producing conditions – Powell 2 is a flowing well, while the Musser-Davis is a gas-lift well. Pre-treatment lab tests demonstrated that Chem-Tec’s PAC-91 product would be effective in re-suspending paraffin and posed no formation damage problems.

A unique paraffin-asphaltene chemical. Chem-Tec LLC’s proprietary paraffin-asphaltene chemical works via unique mechanisms. It raises the temperature of the fluid, by as much as 30 – 40°F, when it encounters brine in the well. Exact mechanisms responsible for the thermal reaction are not known, but it is known that all parts of the blend must be present for the reaction to occur. Bench tests indicate that the elevated temperature remains above ambient for a couple of hours. Field data regarding length of the elevated temperature period is not available. Once treated, paraffin tends to stay suspended.

The product also stimulates microbes naturally present in the brine. Microbial byproducts, such as carbon dioxide and nitrogen, contribute to the observed pressure responses, well cleaning and, with continued microbial growth, longer lasting treatment effectiveness. Unlike some oilfield chemicals, the product does not present handling or environmental challenges. Increased production is the primary benefit, but produced brines also remain cleaner, reducing disposal / injection problems and costs.

In evaluating wells as candidates, Chem-Tec reviews production history, scaling tendencies (product does not affect normal scales, other organic deposits, iron oxide deposits) and samples well fluids (oil, water and preferably, fresh paraffin). Treatments are volumetrically sized, considering static fluid level.

The goal is to achieve 25 – 30% chemical strength and cover the perforations – or, in open hole, the sand face – and achieve a level above that to create weight on the formation to push the chemical into the formation. Shut-in pressures are gauged during treatment. Once they peak, maximum effectiveness has occurred. If the well has recurring paraffin problems, circulation to clean the production string is not recommended.

Powell 2. MOCO’s Powell 2 well produces from the Upper Wilcox from perforations at 10,858 – 10,866 ft. Being located high on structure, Powell 2 should have been the best performing well in the field, but production had been disappointing even after a frac treatment. Problems have been experienced with sand moving into the wellbore and paraffin. Before treatment, production had declined to the 3 – 5 bopd range and, in mid-2001, the well once again became blocked. Because there was a wetting effect with the product and no concerns about damage, MOCO decided, when cleaning the well, to stimulate it. The well was treated in July 2001.

MOCO used coiled tubing to clean the hole, using oil as the carrying agent since the formation is susceptible to damage from low chloride brines. MOCO spotted two, 55-gal drums of the product across the perforations and bull-headed the treatment into the formation. The reaction was immediate when the product hit the formation. There was a 1,000-psi reduction in pump-in pressure, which is contrary to historical experience that pressure increases when pumping into the Wilcox. Normal pump-in pressure in Powell 2 is 6,300 psi. Pressure broke back at 2,500 psi to 1,500 psi. At this point, the well was shut in for 24 hours. When brought back on line, production increased dramatically to 15 bopd. It climbed further and has since stabilized at about 26 bopd.

Musser Davis 3. The Musser Davis 3, which was drilled in 2000, also produced from the Upper Wilcox. After fracturing, it produced only 5 – 8 bopd. Based on positive experience with the Powell 2, MOCO decided to stimulate the Musser Davis 3. Coiled tubing was used to spot one drum of chemical (all that was available then) across the perforations at 10,803 to 10,814 ft. The pressure drop on contact mirrored Powell 2 results. Similarly, production increased to about 30 bopd and is holding steady.

Economics. Treatment costs, including chemical and well work / coiled tubing, averaged $20,000. Chemical represented about 13% of treatment cost for the Powell 2, and half that for the Musser-Davis. Considering the production increases (20 or more bopd per well) and the treatment costs, payouts occur in three months or less. Significantly, production increases more than six months after the treatments are holding relatively steady. MOCO operates 19 Wilcox completions in Southeast Louisiana. MOCO now considers this chemical part of its normal treating program, although no additional wells have been stimulated. When stimulating future wells, MOCO plans to use larger treatment volumes (4 – 6 drums).

Field database. PAC-91 was first marketed in 1991, following a two-year development effort. The first two wells, which were treated in 1991, were in Pennsylvania. In these wells, differences in crude characteristics (dark green and frothy, versus black and not active) were still observed in 1997. To date, there have been about 40 well treatments, with half being in Louisiana and half in New York and Pennsylvania. Different blends have been or are being developed for different regions in the country. PTD