Downhole Splitter in the Gulf of Mexico: Field Introduction and Results
Authors: Hall Douglas , Gardes Robert 
Published: October 2008

ABSTRACT
A down hole splitter wellhead system was successfully introduced and field tested offshore in the Gulf of Mexico south of Mobile Bay. This system is used in a novel process to drill, ease, and complete two independent wells in one wellhead housing. Each well can be produced, serviced, and worked over as a completely separate unit (ref. 1,2).
One well was directionally drilled at 45 deg. into a producing zone while the other well was horizontally drilled into a completely different zone.
Actual vertical and horizontal well sections are presented. These clarify the nature and the extent of the holes that were drilled. One of the holes came up dry, provoking greater examination of contingency methods and solutions.

APPLICATION
By completing two or more wells in a single wellhead housing the splitter design offers advantages over traditional designs. The down hole splitter system can reduce the size of a platform being planned, or it can effectively increase the number of wells per slot recoverable from an existing platform. The design is particularly well suited to wells with multihorizon or multilateral completions, In addition to offshore usage, splitter wellhead systems may be used in inland waters or environmentally sensitive areas.

INTRODUCTION
Conventional wellhead design includes a single well completion from a single wellhead and wellbore. Multiple wells require multiple wellheads, side by side, as shown in Figure 1.
In the conventional design conductor pipe supports the wellhead, the BOP?s, and eventually the tree. The wellhead supports internal casings which form the well, which isolate shallow formations, and which are the "receptacle" for the completion equipment.
The downhole splitter method uses a novel downhole device precisely coordinated with matching novel surface wellhead equipment to utilize the conductor casing and wellhead more efficiently by housing two (or more) production casings in a common wellhead base (Ref.3). See Figure 2.
It must be emphasized that the splitter system is not the same as a conventional dual completion. A conventional dual isolates two completions and allows for separate tree valves per completion.
By comparison, a splitter system is distinguished in the following two ways: firstly, the use of separate production casing strings and packers provides inherently greater well control and safety, and secondly, the wellhead design and its interfaces at low each completion (packer, tubing, tubing hanger, bonnet, and tree) to be as accessible, separable, and serviceable as in two conventional single wells.

DOWNHOLE SPLITTER STACKUP AND OPERATION
The sequence of splitter operation is described with reference to Figures 3 through 9. The sequence shown depicts equipment tailored for the actual offshore well; that is, no base plate was used.
The operator drives 30" in accordance with normal practice, then installs the diverter. The 30" casing incorporates a weld ring with an internal shoulder. Drilling then proceeds for the hole for the 20" casing.
In Figure 3 the operator lowers the permanent portion of the downhole assembly, the splitter head, through the diverter and into the hole.