RIASSUNTO
Abstract
In view of low possibility across fractures, low controlled reserve for a single well, fast production decline, poor development performance for conventional horizontal well and directional well in the liaohe buried-hill migmatitic granite reservoir with characteristics of deep buried-depth, hard rock formation, fractured low porous and permeability, optimization deployment of variety of multilateral wells increases effective footage in pay zone and achieves better development performance by the spatial distribution of several lateral boreholes in a single well. Many challenges such as casing cutting, suspended sidetrack drilling in open hole and retrieving whipstock in this formation are solved, and that delivers records of window opening at the formation in scale of hardness 8, deepest window depth of 3523m. As of today, 40 multilateral wells have been completed with effect improved 3 times as offset vertical wells, 1.5 times as horizontal well. It becomes an approach to develop such reservoirs due to huge economical benefits.
Introduction
Deep paleo-burial hill reservoir has been focused as one of important subsequent reservoirs to be developed for Liaohe oilfield which has come into middle and late stage after the development for over 30 years. Deep buried depth (range from 1500 to 4500m TVD), hard rock, fractured and low permeability and porosity are the characteristics of Paleo-burial hill migmatitic granite reservoir, whilst low reservoir formation drilling ratio, low controlled reserve in a single well, fast production reduction, and poor production effect are common for conventional horizontal and directional well.
With the advancement of drilling and completion technology, special well trajectory and non-conventional wells with many laterals are frequently used in oilfields. Multilateral well is evolved from horizontal well, which achieves the objective of drilling through reservoir with multiple laterals drilled from one main bore incorporated with core techniques as sidetracking from casing, suspended drilling in open hole and tied-back from laterals to the main hole. Main economic and technical advantages in such reservoir are as follows:
- Increase effective footage of single well in reservoir by more laterals under no added horizontal length circumstance.
- All laterals are drilled as crossed in plane and many differentials vertically with spatial distribution in block fractured reservoir, which increases greatly the possibility to drill through the fractures where the oil is.
- Save the cost of land lease, pre-drilling, drilling and cementing of upper section above sidetrack point, production management, surface gathering and so on.
The multilateral wells drilled in burial-hill reservoir of liaohe oilfield are categorized as fish-bone multilateral horizontal well and multilateral with plurality of laterals.
Fish-bone multilateral horizontal well
It is a well where several fishbones as drainage passage are drilled from one horizontal section. Adding horizontal section length to improve drainage passage is sometimes restricted because of limited extended horizontal range in some horizontal wells. However, a few laterals drilled from horizontal section can be easy to achieve without adding flow resistance on way and helpful to drain uniformly. Generally, completion level 1 or 2 is chosen, the challenge is sidetrack drilling technology.