Increasing Performance of Multilateral Wells Using Oil Fingerprinting

Abstract

In multilateral wells, several distinct processes including sand production, mechanical failure, and pattern depletion can cause a decrease in overall well performance over time. Within a lateral, sand can fall out from the production stream and form sand bridges that obstruct production from that lateral. In addition, sand co-produced with oil from shallower laterals can settle through the production stream to obstruct the entry to a deeper lateral. However, a decrease in production cannot be assumed to be due to obstructions formed by co-produced sand, since a variety of completely different processes can also reduce production. It is critical to know the cause of decreased production from a well, since which method is used to reverse the decrease in production very much depends on the cause of the decrease.

Geochemical techniques can be used to quantitatively determine the contribution of each of several zones to a commingled oil (or gas) stream. This technique costs less than 1-2% of the cost of production logging. One particularly useful application of this technique is using oil fingerprinting to identify sanded-out intervals for fill cleanout (FCO)

In brief, production allocation is achieved by identifying chemical differences between end-member oils (single-zone samples collected from each of the zones being commingled). Parameters reflecting those compositional differences are then measured in the commingled oil. Those data are then used to mathematically express the composition of the commingled oil in terms of contributions from the respective end-member oils. That result is achieved using a linear algebra manipulation of the concentrations of 150-250 compounds naturally occurring in the end member oils and the commingled oils.

In the current study, we show three examples where this approach was used to identify a sanded out interval in each of three wells. Once the sanded-out interval was identified, an appropriate FCO operation could be conducted. This approach resulted in increased production of 200 BOPD, 500 BOPD, and 400 BOPD in the three respective wells. For those wells, the cost of the geochemical analysis was less than the value of 1 hr of increased oil production.