Well Completion Design and Operations for a Deep Horizontal Well with Multiple Fractures

Abstract

Abstract Economic development of deep tight gas reservoirs is a challenge our industry has struggled with for many years. This paper describes how a very deep (15688', 4783 m TVD) well with a horizontal section (over 86) of over 630 m (2,066') was completed for stimulation with multiple fractures. Multiple packers and sliding side doors provided isolation for 4 separate fracs and a 5th zone containing 52m (171') of perforated interval in the 7" casing. Extreme overbalance perforating techniques using tubing conveyed perforating guns and high pressure nitrogen were used to perforate and break down each of the 0.6m (2') of perforated intervals for the 4 fracs and 853 perforations in the 5th unstimulated zone. To achieve a high shot density, a special perforating tubing anchor was designed to allow two different perforating guns to perforate exactly the same interval in one trip. An open annulus treating system was used with a 4 1/2" frac string for observation of the bottomhole treating pressure during fracture operations. A total of over 2 million pounds of high strength proppant was pumped into the 4 fracs at rates in excess of 5.6m3/min (35 BPM). High bottomhole temperatures (290 F, 143 C), reservoir pressures (9000 psi, 620 bar), and bottomhole treating pressures (16000 psi, 1100 bar) added to the complexity of design and operation of equipment. Over 5,700 m (18,700') of 1 3/4" coiled tubing was run to TD and used in conjunction with a downhole force generator to open and close the sliding side doors. Introduction Mobil Erdgas-Erdoel GmbH has recently drilled, cased, and fracture stimulated the very deep horizontal well, Soehlingen Z-10, in an ultra-tight Rotliegendes sand at a TVD of 4,783m (15,688') in North-West Germany. Mobil is the operator of a consortium that includes BEB Erdgas und Erdoel GmbH, RWE-DEA AG and Wintershall AG. The well was drilled to a TD of 5,750m (18,860') including a 630m (2,066') horizontal section and four hydraulic fractures. The multiple frac concept was used in order to develop a cost-efficient method to economically produce significant gas resources from the tight sand. Mobil, as operator, began developing Soehlingen in 1982. The tight reservoir has been produced on a limited basis from three vertical wells drilled in the early 1980's and fractured with conventional techniques, i.e. with large fluid volumes (500,000 gallons of crosslinked fluid), with 35% by volume pad, and up to 7 ppg proppant concentration. Results of the treatments were mixed. The resulting low rate, 4.5 MMSCFD, was sustained for more than six years but proved uneconomical. To improve the economic viability of this significant resource base, Mobil sought to combine two technologies, horizontal wells and hydraulic fracturing. The challenge was to provide a horizontal completion design which would facilitate multiple hydraulic fracturing in a very deep, long horizontal well. Design Requirements In preparation of the completion design, numerous meetings were held by the project team to determine the reservoir, stimulation, testing, and evaluation requirements for the completion design. From these meetings the following criteria were developed: P. 499