Single drilling guide base for subsea oil wells

A single drilling guide base for subsea oil wells includes two parts, namely a lower part (1) and an upper part (2), which are bolted together (at 7). The whole arrangement is provided with a seating indicator (5) connected to the lower part and holes in a funnel shaped portion of the upper part for the discharge of gravel.

BACKGROUND OF THE INVENTION 
The invention relates to a piece of equipment to be installed on the sea 
bed for subsea oil well drilling. More specifically, the object of 
invention is to provide a single structure to be installed on the sea bed, 
intended to serve as a base for subsea oil well drilling work. 
The discovery of oil fields lying within continental shelves has led to the 
development of new techniques in the drilling of oil wells. Throughout the 
years new equipment and methods of work have been developed by the 
specialists for the purpose of facilitating the difficult task of drilling 
for subsea oil. 
Starting from simple adaptations of equipment used for onshore work, subsea 
drilling techniques have developed to the point of having to call into 
play highly complex equipment, very different from that employed onshore, 
and requiring the efforts of specialists endowed with a high degree of 
technical knowledge. 
Among the various kinds of equipment developed for enabling subsea oil 
drilling to take place, those known as drilling guide bases are a typical 
example of the progress that has been made in subsea drilling techniques. 
A drilling guide base is fastened to the first casing of a well driven in 
the sea bed and serves several purposes including the guiding of other 
nearby well casings to ensure a vertical well. The consequences can be 
serious if a drilling guide base fails to ensure that the various casings 
are properly vertical. 
The first guide bases developed to meet the requirements of oil subsea 
drilling work comprised largely two structures. 
The first was referred to by the specialists as a temporary guide base and 
was laid on the sea bed coupled to the well pipe casing. Though it is 
provided with devices for offseting tilting, its natural tendency is to 
match unevenness in the sea bed, which is of course not desirable because 
in doing so it will make vertical well drilling difficult. 
As a way of overcoming this drawback a second structure, referred to by the 
specialists as a permanent guide base, was laid over the temporary one. 
This second guide base had devices intended to offset any tilting of the 
temporary guide base. 
Brazilian application PI 8700104-7 shows a typical example of a guide base 
made up of temporary and permanent bases, where the permanent guide base 
rests on the temporary guide base by means of a semi-spherical surface 
correcting any tilting that may have taken place when the temporary guide 
base was laid. 
Brazilian application PI 8900855-3 introduced an inovation by proposing 
that a single guide base be employed to guide subsea drilling operations, 
and enabling vertical wells to be drilled regardless of the unevenness of 
the sea bed. 
This single guide base comprises a cylindrical structure which has in its 
upper, part a funnel to guide the descent of the pieces of equipment into 
the well. To give strength to the assembly and to enable it to be put in a 
vertical position, a driven pile is jetted into the sea bottom, all of 
this operation being monitored by television in a remote operated vehicle; 
the slope of the assembly being controled with the aid of a level 
indicator. 
The next step is to install the low-pressure housing with its casing. This 
low-pressure housing is placed upon another housing previously bolted 
to,the base. Then the casing is cemented. 
Next the well is drilled, after which the head pressure housing and its 
respective casing set and finally cementing is carried out, all of which 
provides a firm base to support the other casings to be installed in the 
well. 
This single guide base has brought about great progress in well drilling 
techniques and has led to considerable savings because it has done away 
with certain parts and expensive operations. However, there are still some 
shortcomings, of which the principal one concerns the large size of the 
arrangement which makes hauling and installing very difficult. 
SUMMARY OF THE INVENTION 
The present invention makes significant alterations to the single guide 
base in subsea drilling for oil, making it lighter and more efficient as 
well as creating devices that enable better monitoring of the laying 
operations. 
The invention relates to a single guide base used in the drilling of oil 
wells, whereby the low pressure housing is mounted directly to the guide 
base thus doing away with the need for another housing to ensure 
sturdiness of the arrangement. 
Accordingly, the present invention provides a single subsea oil well 
drilling guide base comprising a lower part bolted to an upper part whose 
top surface is funnel-shaped for helping to guide down equipment and tools 
used in the well drilling stage; wherein said guide base is provided with 
bolts to hold a housing and with holes to enable gravel drilled out to 
issue from inside the base before the well casing is installed. 
The lower part may be provided with a device to show how the arrangement is 
being seated, which enables a better view of the operation in a remote 
operated vehicle by means of a television circuit.

DETAILED DESCRIPTION OF THE INVENTION 
Before starting to describe the invention, reference will first be made to 
FIG. 1 in which can be seen a prior art subsea oil well drilling guide 
base. 
This drilling guide base comprises a lower part 10, which acts as a 
support, an intermediate cylindrical part 11 coupled with the lower part 
10, an lower cylindrical part 19 which is coupled with said intermediate 
cylindrical part 11, and a funnel-shaped upper part 22, superposed on said 
upper cylindrical part 19 and intended to guide tools down into the well. 
A housing 12 is bolted to the intermediate cylindrical part 11 by means of 
bolts 13; a pipe 14, referred to by the experts as a conductor is 
connected to said intermediate cylindrical part 11. A second intermediate 
housing 17 is mounted on the housing 12, with its respective pipe 15 which 
is also known as a conductor. Finally a high pressure housing 18, with its 
respective pipe 16, is mounted on the intermediate housing 17. 
The guide base is fitted with a level 20 which enables the verticality of 
the assembly to be checked by means of a television circuit of a remote 
operated vehicle. Holes 21 are provided in the lower part for the 
discharge of gravel. 
The guide base described above was a big step forward in the subsea oil 
well drilling techniques but it still suffers from some shortcomings. The 
use of two housings with their respective conductors means that its size 
and weight are considerable, which makes it rather awkward to ship, 
whether from the point of construction to the quay side fop shipping, or 
whether from the instant of off-loading on to a supporting vessel up to 
the time of delivery to a drilling rig that is to install it. 
Another point to be borne in mind is the increase in cost due to the use of 
two housings and their respective conductors, not to mention the extra 
cost incurred through longer use of a drilling rig to lay the two 
housings. All these costs add up to a great amount. 
FIGS. 2 and 3 show an embodiment of a single guide base according to the 
present invention. 
The two parts, the lower part 1 and the upper part 2, are bolted together 
by bolts 7 thereby making up the body of the guide base. This is rather an 
important feature of the guide base for it enables the lower part 1 and 
the upper part 2 to be easily carried separately to whatever place is most 
suitable for them to be bolted together, thereby considerably lowering the 
cost of shipping and also the time needed for the job. 
A housing 3 with its casing pipe 8 is mounted on the guide base body, said 
housing 3 being bolted to the guide base by means of bolts 6 as shown in 
FIGS. 2 and 3. The assembly is then fixed to the sea bottom, preferably by 
jetting, in such a way that casing 8 sinks gradually in until the lower 
part of body of guide base is resting on the sea bed. 
In order to ensure that the gravel arising out of the drilling process does 
not heap up and hinder the observation and monitoring of the operation, 
there are holes 29 in the upper part 2, intended to let gravel out of the 
lower part of the guide base, thus preventing it from gathering there. 
FIGS. 2 and 3 show a seating indicator rod 5, coupled together with the 
lower part 1, this being just a longitudinal part 25 of any 
cross-sectional shape, fitted into a small segment of a tubular guide 26, 
which is smaller than said longitudinal part 25. The longitudinal part 25 
is provided at its top and bottom with stops 27 and 28, which are bigger 
than the outer diameter of the tubular guide 26 so that the longitudinal 
part 25 may travel freely within tubular guide 26 without escaping, since 
prevented by stops and 28. 
FIG. 2 shows the indicator rod 5, in the position it occupies before it 
touches the sea bottom, and FIG. 3 shows its position after guide base has 
been laid place. 
The purpose of the indicator rod 5 to enable the operator to be sure that 
job has been done properly. The operator watches over all the laying of 
the guide base by means of a television circuit in a remote operated 
vehicle. Just watching, without the use of an indicating rod 5, will not 
be enough to ensure that the guide base is actually contact with the sea 
bed since gravel which usually gathers around the place where the guide 
base is being installed could possibly mislead the operator into believing 
that the guide base is resting on the sea bed when really it is only lying 
on top of such heaped-up gravel. 
In such cases, that is, where the operator finishes sinking the casing into 
the sea bed having been convinceded that guide base is properly seated, 
the consequences can turn out to be disastrous, for the soundness of the 
whole arrangement will be threatened, and the stability of all equipment 
to be installed over the guide base will be prejudiced. 
By using the indicator rod 5, it becomes a lot easier for the operator to 
know when the job really is finished, for all he has to do is to watch the 
indicator rod 5 to have reliable information about the job. As soon as the 
longitudinal part 25 touches the sea bed it becomes pushed upwards, 
sliding freely within the tubular guide 26, as can easily be seen by the 
operator watching it rise. 
Once the single guide base for drilling into the sea bed has been properly 
laid, actual drilling of the well can begin. FIG. 3 shows the while well 
head assembly already in place, with its high pressure housing 4 mounted 
on housing 3, and the casing 9 also connected to the aforesaid wellhead 
high pressure housing 4. 
All this serves to show that the subsea oil well drilling guide base of the 
present invention is very useful, for it is cheaper to make, easier and 
less expensive to ship, and much simpler to install, thereby helping to 
cut down even more the final cost of subsea oil well drilling work.