Specialized Pumping Techniques Applied to a Very Low-Gravity, Sand-Laden Crude - Cat Canyon Field, California
Authors: Vonde Thomas R. 
Published: December 2007

With the application of specially designed pumping and treating equipment, we are producing crude oil as low as 4°API (1.044 g/cm3) containing up to 70 vol% of sand. An important part of this system is the bottom hole pumping equipment that has allowed primary production rates in excess of 150 B/D (24 m3/d) oil from wells that were restricted to less than 10 B/D (1.5 m3/d) oil when produced with conventional rod pumps and sand control completion methods. These pumps are available commercially.

Techniques developed may be extended to other areas where production is limited by problems inherent with highly viscous crude oils and excessive sand entry.

Introduction

Problems with pumping extremely viscous crude oils are well known to all operators who produce low-gravity crude oil. Rod floating, overloaded pumping units, and pumps plugged with heavy crude oil are common occurrences. Likewise, such problems as stuck pumps, eroded tubing and sucker rod couplings, and stripping jobs are common wherever sandy production occurs. We experienced all these problems in producing the Brooks reservoir, located in the Cat Canyon field, Santa Barbara County, CA, where oil gravity averages 6°API (1.029 g/cm3), and the production contains up to 70% sand. Over a 5-year period these problems were ameliorated with the development and successful application of special downhole pumping equipment. This paper up-dates a previous work on this topic.1

The Brooks reservoir sand is an unconsolidated basal member of the Pliocene Sisquoc formation. The sand is very fine-grained and well-sorted, with a medium sand-grain size of 0.0065 in (0.165 mm) and a Trask sorting coefficient of 1.2. Reservoir depth ranges from 2,500 to 3,500 ft (760 to 1070 m); average net sand thickness is 150 ft (46 m). A type log is shown in Fig. 1. There is no significant primary water production, and the zone produces at less than 1 to 2 % water cut, except where wateror steam injection has occurred.

The oil gravity of Brooks zone is among the lowest produced in the world, and ranges from 11 °API (0.993 g/cm3) in the upstructure area to about 0°API (1.076 g/cm3) downstructure at the reservoir limits. Reservoir oil currently averages about 6°API (1.029 g/cm3) and has 15,000-cp (15-Pa·s) viscosity at reservoir conditions.

Reservoir properties of the Brooks sand and fluids are summarized in Table 1.

Operating Experience With Conventional Equipment

Production from the Brooks zone began in 1909 in the area where highest oil gravity occurs. These early wells were completed with 250-mesh [0.25-in. (6.35-mm)] slots or 1/2-in. (12.7-mm) holes through the zone, which allowed almost unrestrained sand production from the unconsolidated formation. Initially, these wells flowed up to400 B/D (64 m3/d) of 10°API (1.0 g/cm3) oil containing about 15 % sand. Cumulative recovery from this old part of the field is now more than 10% of the OOIP. Individual wells have produced over 400,000 bbl (64 000 m3) of oil and 40,000 bbl (6400 m3) of sand over a 40-year life. To pump the highly viscous oil with conventional pumping equipment it was necessary to inject a distillate into the wellbore, which blended the native oil up to about 12°API (0.968 g/cm3).