Horizontal Gravel-Packing Technique for Slim, Cased Holes in Highly Permeable Zones: A Single-Well Case History

Abstract

Summary This paper describes a technique for horizontal gravel packing of slim, cased holes. The key to the technique is the use of horizontally oriented perforations as a means of providing self-diversion of the gravel pack regardless of fluid leakoff. Traditional horizontal gravel packing requires minimizing fluid leakoff to the formation; otherwise, premature bridging can occur during the gravel-packing process. The cased hole horizontal gravel-packing process presented here, however, does not require minimizing fluid leakoff to the formation, thus, allowing the possibility of placing a gravel pack in a horizontal casing with less resultant damage than is possible with traditional techniques. Gravel packing is becoming a common practice for controlling unconsolidated sands in horizontal wellbores. So far, horizontal gravel packing has been applied almost exclusively to open holes with screens in them. If a formation has a high permeability, and therefore, a high fluid-loss rate, placement of a gravel pack may be prevented by premature dehydration and bridging of the gravel-pack sand in the wellbore/screen annulus. The usual method of preventing these high fluid losses and the resultant bridging is to damage the formation face prior to gravel packing. The damage mechanism is usually salt, calcium carbonate, or other particles that seal off the formation face. Once gravel packing is completed, the formation damage is (hopefully) remediated using acid or undersaturated brines to restore the completion's productivity. There is, however, a risk that the damage cannot be successfully removed once it is gravel packed against the formation face. Acid diversion is also a problem when attempting to remediate damage in an openhole gravel-packed completion. This paper presents an alternative technique for performing a horizontal gravel pack in a high-permeability zone while reducing the risk of permanently damaging the formation's permeability. The technique involves cementing casing through the horizontal completion interval and then shooting perforations in a horizontal orientation. The perforations can then be acidized with better diversion techniques than is possible in an openhole completion. An uncentralized screen is then gravel packed. The horizontally positioned perforations provide a self-diverting gravel pack. The self-diverting nature of this technique makes it relatively insensitive to fluid loss; whereas openhole techniques are very sensitive to fluid loss. The uncentralized liner rests on the bottom of the horizontal to provide maximum standoff from the perforations. The above technique was applied at Thums Long Beach Company to a well with a 560-ft horizontal completion cased with a 412-in. liner (4.052-in. ID). The technique's acidizing phase, however, was not performed due to fishing concerns inside the slim liner. This paper presents a case history for gravel packing a 690-ft-long, 278-in.-slotted liner inside the horizontal 412-in. casing. To our knowledge, this is the slimmest horizontal gravel pack ever attempted. The gravel packing was performed successfully even though fluid returns were never established during the job. The lack of fluid returns is due to excessive fluid loss to the formation. The self-diverting nature of the horizontal perforations was the key to successful gravel packing. Production rates, on the other hand, were not as successful since we did not acidize the perforations prior to gravel packing. Comparisons between this well and openhole horizontal gravel packs are made.