Coiled Tubing Workover Saves Horizontal Well in Lake Maracaibo
Authors: Lizak Ken. , Patterson James , Suarez Diego , Salas Jose 
Published: October 2008

A slotted liner horizontal completion became stuck while being run. Inflatable packers were to be used to isolate the productive interval from a water-bearing, unconsolidated sand in the curved section of this well. While personnel were deciding how to cemenl the well, the liner was left in the hole with the inflatable packers unset, and [he production tubing was run. Coiled tubing was used to log the well, isolate the productive interval, and remove damage to restore well productivity.

Personnel considered all possible options, and a thorough decision-making process guided the workover. Because of severe lost-circulation problems, extensive 'what if' scenarios were made and updated daily for the engineers on location. Service company and oil company personnel worked together to guarantee the job designs were practical and did not exceed the limits of the equipment on location. Computer simulations of all operations were run to allow corrective action to be taken if unusual circumstances arose.

All fluids were thoroughly laboratory tested and witnessed by oil company personnel to ensure job success.

Problems on the job included lost circulation, locating the exact positions of the packers and water zone, ensuring correct cement placement, removing mud and workover fluids without damaging the squeeze, and bad weather on Lake Maracaibo. Advantages and disadvantages of all the solutions that were considered are included to assist anyone in a similar situation.

Post-job oil production has stabilized at 900 BOPD with no water or sand production. Careful job planning and the versatility of coiled tubing saved this well and proved economical with an estimated payout of 33 days, assuming a price of $12 per barrel of oil.

Introduction

The productive intervals in the Bolivar Coastal field of the Lake Maracaibo basin generally consist of three productive horizons. The deepest Cretaceous formations range from 14,000to 11,000 ft. The Eocene-age formations are sandstone and range from 11,000 to 4,000 ft depending on the area. These rocks tend to be consolidated with varying permeability, usually low to medium. Many of these formations need to be hydraulically fractured to be economical. The Eocene section is split into as many as 16 different reservoirs, delineated by sealing shales. Above the Eocene section is an unconformity that is overlaid with unconsolidated Miocene-age sands. Severe sand production problems are often encountered in these unconsolidated formations.

In the area in which this well was drilled, the unconformity between the unconsolidated Miocene and the consolidated Eocene formations is located at approximately 6,680 ft. In this area, the La Rosa formation, which is wet, lies just above the unconformity. This well was originally completed in October 1956 as a vertical producer in what is known as reservoir B-6- X.30. The perforated interval was from 6,805 to 6,905 ft. In early tests, the well produced more than 3,000 B/D, with production declining as water cut increased. In 1960, production had fallen to 1,082 B/D with 40% water. The well was subsequently squeezed and reperforated in the top 13 ft of the formation. Production after the squeeze was more than 2,000 B/D with a6% water cut, Water production continued to increase, possibly caused by water coning.