With a long history of drilling vertical wells aiming at producing hydrocarbons from several different pay intervals, the Lake Maracaibo Basin has reached a stage of maturity that requires resorting to new technologies to overcome problems normally found in basins at this stage of development. Horizontal drilling provides a means to increase recovery, drain individual sands more efficiently and thoroughly, avoid negative effects like water coning or finguering resulting from fast production, and, shortening producing periods by recovering reserves more rapidly. Miocene sands where this technology was applied, presented several intervals of unconsolidated sands of variable continuity, pay intervals with most frequent thickness in the ten to twenty feet range and reservoir pressures predominantly at hydrostatic or below hydrostatic values.
The horizontal drilling program in the Lagunillas Lago Production Unit of Maracaibo was initiated in 1995. To date, 91 wells have been drilled with a total horizontal footage of 94,173 feet drilled. Results can be assessed only through an economic analysis in which time plays an important role. Pay out. Profit to Investment Ratio and Net Present Value properly discounted, are some parameters used in the evaluation of horizontal wells. For instance, of the 18 horizontal wells drilled in 1996, 42% show less than a 2-year pay out. 42% a pay out of 2 to 4 years and, 16% a pay out of more than 4 years. Profit to Investment Ratio for the same time period was distributed as follows: 68% greater than 2, 21% between 1.5 and 2, and 11% less than 1.5.
Future horizontal drilling will be dictated by volumes of Remaining Reserves combined with performance of vertical wells in the same area. Vertical wells showing high water cuts will be considered for replacement by horizontal wells, provided that Remaining Reserves justify investment. Because of the low pressures in many reservoirs, formation damage by drilling fluids will be carefully assessed. Dual horizontal drilling in heavy oil reservoirs, in combination with steam injection, will be an important consideration in future programs.