A new tool was adapted to clean out sand from the bottom of oil wells; it is a mix between a subsurface sucker rod pump and a bailer. The tool is run into the hole by drill pipe, it is easy to handle and does not need external fluid to operate. Among the advantages of the new oil well clean out tool (HDP), compared with the traditional clean out methods such as circulation and wire line tools, the HDP can be used for depleted wells and for removal of large amounts of sand. Also, there is not formation damage due to the fact that no external fluid is injected, and the frequency of clean out jobs for critical wells has decreased from two per year to one per year. Excellent results have been reported in more than one hundred clean out jobs up to date. This paper briefly describes the steps followed during the development of the HDP tool.
The production fields of the El Centro, Colombia, has some formations with non consolidated sand. Sand is dragged by the formation fluids -oil, gas, water-, carried out through the casing and tubing and settle down in the bottom of the well. By the time, the casing gets full of sedimentary solids, the production zone becomes plugged and the bottom sucker rod pump gets stuck, workover activities has to be done to put back into operation the well. On average, a clean out operation is required every 8 months for each wells; a lot of effort, money and time is put into these workover activities.
There are two conventional methods used to clean out the sand; fluid circulation and wire line tools. The circulation method consists in the injection of an external fluid from the surface, throw a collar tubing, to the top of sand. The fluid returns to the surface through the annular between the collar and the casing, lifting and carrying out to the surface the solids settled at the bottom. Then, on surface, the solids are separated from the workover fluid. There are several types of fluids, such as, treated water, brine, oil, gel, foams, etc., all of them require to be prepare adequately to avoid damages to the formation. On the other hand, wire line tools take advantage of a storage chamber that is assembled on surface at atmospheric pressure, then the tool is run into the hole to the top sand, where the chamber is opened to allow the entrance of fluid and sand into the storage chamber. The well head pressure is the force that induces the entrance of the mix.
The circulation method on depleted fields produce damages to the formation due to its contact with external fluid. Also there is an incomplete removal of solids, because during the cleaning process a given amount of solids are carried into the formation, then when the well is put into operation, these solids come out again to settle down in the bottom of the well. Besides, some wells require a lot of working fluid during the cleaning process because it is absorbed by the formation, then when the well is put back in operation, it is necessary to allow more time for the well to reach normal production. Wire line tools are inefficient when the deposited sand is compacted and there is a large amount of it to be cleaned out.
Due to the frequency of sand clean out jobs in many wells in the field El Centro and to local problems related with unconsolidated and depleted formations, a new tool was designed to over come the disadvantages found with the circulation method and the wire line tools. This tool do not use external fluid, has good cleaning capacity in each run, and it is easy to operate by the workover people.
Development of the clean out oil well sand tool.
Looking for an alternative, the market was explored and some tools were run in some wells but the results were not as good as expected. Considering the experience with these tools, there was the need to come up with a new design. An acrylic pilot well of 5 meters of length was built (Fig. 1) to simulate and analyze the sedimentation process of sand in different fluid viscosities and sand grain sizes. This pilot well, in combination with a pilot tool, were also used for studying the fluid-dynamic behavior of the tool under design.