Application of Horizontal Well Technology in Colombia
Authors: Saavedra N.F. , Joshi S.D. 
Published: March 2010

Abstract
To date, 20 horizontal wells have been drilled in Colombia: 16 in sandstone, and four in carbonate reservoirs. In carbonate, the economical success rate is 50 %, but in sandstone it is 88 %.
In general, wells in Colombia are expensive. The vertical well cost varies from $2 million to $11 million, depending upon the reservoir depth. Horizontal well costs vary from 1.5 to 2.5 times the vertical well costs. Initially, most of the wells were completed with slotted liners. Now, new wells are completed with cemented and perforated liners to control water and gas production. The range of True Vertical Depth (TVD) is between 914 m (3,000 ft.) and 4,880 m (16,000 ft.).
This paper presents three brief field histories, and the lessons learned to date. In cases where production is less than expected, the principal causes are:A horizontal well has commingled production from zones of high contrast in permeability, reducing considerably the producing length of a horizontal well.Production of unwanted fluid such as water and gas. With slotted liner completion, it is not only difficult to identify gas and water producing zones, but it is also difficult to isolate them effectively.Geological uncertainty, which results in drilling a well through a zone which is geologically different than expected.
New horizontal wells are planned as short length wells in high permeability zones, and long ones in low permeability zones. Also, re-entry wells are now used in mature reservoirs to reduce drilling costs.
The method used to analyse the well performance is discussed in the paper. To determine the producing length, gamma ray analysis, log information, production tests and/or production logs were used. A productivity analysis using analytical equations was also conducted to define if the well was damaged or had a small producing length. Then, decline curve analysis was used to forecast rate and reserves, and well production histories were matched for rates and cumulative production over time. Depending upon the problem, and considering feasibility and cost effectiveness, a corrective action was designed to improve well productivity.
In summary, horizontal wells in Colombia have been successful and a large potential exists to drill many more wells.

Introduction
The history of horizontal wells in Colombia began in 1991, with the attempt to drill the well Orito 1H (it did not reach the objective because of operational problems). In January of 1993, the well Chuchupa 14 was successfully completed in a gas reservoir with higher than expected production(1). Then, in 1997 the well Guatiqu?a 3H was drilled in the Apiay Reservoir(1). It had some operational problems, but had excellent productivity results. Since then, another 18 wells have been drilled in different Colombian reservoirs.
Out of 20 horizontal wells, four wells have been drilled in carbonate reservoirs, and 16 have been drilled in sandstone reservoirs. From the four wells drilled in carbonate reservoirs, one has been economically successful, one is non-economical, and two have too short a history to determine the economics conclusively.