This paper includes a review of horizontal well field histories and applications around the globe, with special emphasis on South and Latin American applications. The paper includes descriptions of economically successful, as well as unsuccessful horizontal wells in field applications. Results of the field histories are used to summarize essential parameters for economic success.

Horizontal wells have been used in: 1) thin pay zones, 2) naturally fractured reservoirs, 3) formations with gas and water coning problems, 4) heavy oil reservoirs, 5) gas reservoirs, and 6) enhanced oil recovery (waterflood applications, miscible floods, and thermal oil recovery).

Out of about 2500 horizontal wells drilled worldwide, almost 75% are drilled in the USA and Canada. In addition, most of the U.S. welts are drilled in a few formations, namely, Austin Chalk and Bakken Shale. Host of the U.S. applications are in low permeability (*1 md) reservoirs.

Outside the U.S., the majority of applications are for gas and water coning, mainly for water coning. These applications are in high permeability (400 md to 10 Darcy) reservoirs. In general, horizontal wells have a higher success rate in water coning applications than in gas coning situations.

Recently, horizontal wells have also been used in secondary recovery applications. Horizontal wells have exhibited excellent results in miscible CO2 floods. While application of horizontal wells in waterflooding shows great potential, application in thermal oil recovery shows mixed economic results.

The key parameters for success, based upon field results, appear to be: 1) fracture intensity, 2) hydrocarbon pay zone thickness, 3) well spacing, 4) vertical coomunication, 5) formation damage and post drilling clean-up ability, 6) geological control, 7) multiwell prospect, and 8) cooperation in geological, reservoir, drilling, and completion departments.

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