Embodiments of the present disclosure generally relate to a downhole motor-pump assembly.
It is known within the prior art to use a downhole motor (e.g., a drilling motor) and/or a downhole pump disposed within a drill string. In many situations, however, the design of the downhole motor is complex and contains numerous components in addition to a stator and a rotor, such as long torsional shaft drives, plungers, wobble shafts, bearings, and/or couplings. Additionally, the downhole pump is usually a separate component from the downhole motor. Consequently, there is a need for a simpler downhole motor-pump assembly, especially where the motive and pumped fluids can be combined before the pump discharge.
A first embodiment of the present disclosure is a downhole motor-pump assembly disposed within a tubular string including a rotor and a stator. The rotor has a first rotor portion and a second rotor portion. The first rotor portion has a first geometrical shape and the second rotor portion has a second geometrical shape. The first geometrical shape differs from the second geometrical shape. The stator has a first stator section and a second stator section. The first stator section is spaced from the second stator section by a gapped region. The rotor is located within the stator and configured to be rotated by fluid flowing downstream within the tubular string.
Another embodiment of the present disclosure is a tubular string including a downhole motor-pump assembly and a string body. The downhole motor-pump assembly includes a stator and a rotor. The stator has a first stator section and a second stator section. The first stator section is spaced from the second stator section by a gapped region. The rotor is configured to rotate freely within the stator. The downhole motor-pump assembly is disposed within the string body and configured such that the rotor rotates within the stator when fluid is urged downstream within the tubular string.
Another embodiment of the present disclosure is a downhole motor-pump assembly including a stator and a single rotor. The stator has a first stator section and a second stator section. The single rotor is positioned within the first and second stator sections. The downhole motor-pump assembly is devoid of any wobble shafts or couplings.
So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
Embodiments described herein relate to a downhole motor-pump assembly disposed within a tubular string. The downhole motor-pump assembly may comprise a rotor and a stator. The rotor may have a first rotor portion and a second rotor portion. The first rotor portion may have a first geometrical shape, and the second rotor portion may have a second geometrical shape. The first geometrical shape may differ from the second geometrical shape. The rotor may be configured to rotate freely within the stator. The stator may have a first stator section and a second stator section. The first stator section may be spaced from the second stator section by a gapped region. The rotor may be located within the stator and configured to be rotated by fluid flowing downstream within the tubular string. In operation of the assembly, the first rotor portion and the first stator section may collectively function as a motor, and the second rotor portion and the second stator section may collectively function as a pump.
The downhole motor-pump assembly 100 includes a rotor 104 and a stator 106. The downhole motor-pump assembly includes an inlet opening 105 and an outlet opening 107. The rotor 104 has a first rotor portion 108 and a second rotor portion 110. In the embodiment shown in
In one embodiment, the rotor 104 may be a single, one-piece element. It is to be understood, however, that the rotor 104 may be comprised of two or more elements coupled together. For example, the first rotor portion 108 may be a first element and the second rotor portion 110 may be a second element, with the first and second elements being coupled together. It is also to be understood that rotor 104 may include more than two rotor sections. For example, the rotor 104 may include a third rotor section positioned between the first and second rotor sections, with the third rotor section being of a third geometrical shape. In such a situation, the third geometrical shape may differ from the first geometrical shape, from the second geometrical shape, or from both the first and second geometrical shapes.
The stator 106 has a first stator section 112 and a second stator section 114. The first stator section 112 is spaced from the second stator section 114 by a gapped region 116. The rotor 104 is located within the stator 106 and configured to be rotated by fluid flowing downstream within the tubular string 102. More specifically, the first rotor portion 108 is located within the first stator section 112 and the second rotor portion 110 is located within the second stator section 114. The first stator section 112 has a first internal profile that is substantially similar to the first geometrical shape of the first rotor portion 108 and the second stator section 114 has a second internal profile that is substantially similar to the second geometrical shape of the second rotor portion 110. The rotor 104 is freely orbiting within the stator 106 and need not be coupled to any further device to perform its function, thereby eliminating the need of any wobble shafts, radial bearings, and/or couplings. A downstream end of rotor 104 rests on a platform 120 of the tubular string 102. Platform 120 may include a thrust bearing or collar to transfer any thrust load of the rotor 104. Note that the common rotor and the port arrangement cause a substantial balancing of thrust forces within the pump and motor assembly, lessening the requirements of the thrust bearing.
The tubular string 102 includes a pump opening 118 located downstream of the downhole motor-pump assembly 100. The tubular string 102 is configured such that the outlet opening 107, the pump opening 118, and the gapped or ported region 116 are fluidly connected to each other to form a localized circulation loop. The gapped or ported region 116 creates a suction force as fluid is pumped downstream through the second stator section 114. The suction force pulls wellbore fluid and debris particles DP located within the well into the tubular string 102 via the pump opening 118. As can be seen in
In operation, the first rotor portion 108 and the first stator section 112 collectively function as a motor of the downhole motor-pump assembly 100, and the second rotor portion 110 and the second stator section 114 collectively function as a pump of the downhole motor-pump assembly. The tubular string 102 is first lowered to a desired depth within the wellbore. A driving fluid may then be urged downstream through the tubular string 102 at a flow rate of, for example, approximately 3 barrels per minute (i.e., BPM), and a pressure of approximately 1000 psi at inlet opening 105. As the driving fluid is urged downstream, it causes the rotor 104 to freely rotate within the stator 106, as the rotor is not connected to the stator via any wobble shafts, bearings, and/or couplings. As the rotor 106 rotates, the second rotor portion 110 within the second stator section 114 displaces a larger volume of fluid per revolution of the rotor than the first rotor portion 108 within the first stator section 112. Consequently, the second rotor portion 110 and the second stator section 114 would generate a suction force at the gapped or ported region 116 to induce the necessary additional flow to satisfy this section's additional flow requirement. The pressure at the gapped region 116 is then for example, approximately 0 psi. The suction force generated at the gapped region 116 creates a flow of wellbore fluid through the gapped region 116 and into the second stator section 114. Because the outlet opening 107, the pump opening 118, and the gapped region 116 are fluidly connected to each other, it generates the previously discussed localized circulation loop that can be seen in
For example, during operation of the downhole motor-pump assembly 100, the flow of additional wellbore fluid passing through the gapped region 116 could have a flow rate of approximately 6 BPM. Consequently, the flow rate of fluid flowing through the second stator section 114 will be greater than the flow rate of fluid flowing through the first stator section 112. For example, the flow rate of fluid flowing through the first stator section 112 may be approximately 3 BPM while the flow rate of fluid flowing through the second stator section 114 may be approximately 9 BPM. The driving fluid urged downstream through the tubular string 102 from, for example, a surface pump is combined with fluid pumped through the gapped region 116. As discussed above, the driving fluid entering the inlet opening 105 may exert a pressure of approximately 1000 psi while the combined fluid exiting the outlet opening 107 may have a lower pressure of approximately 300 psi, but with an inversely proportionate volume increase.
As can be seen in
In this manner, the tubular string 102 and the downhole motor-pump assembly 100 enable the removal of debris from the wellbore. Moreover, the tubular string 102 and the downhole motor-pump assembly 100 provide for the ability to control and monitor downhole performance within the well from a sea surface as a result of the pressures and flow rates seen at the surface correlating to those of the pumped fluid by the downhole pump. This is only possible with such positive displacement pumps. Another advantage of the downhole motor-pump assembly 100 is the reduced fluid pressure of a localized flow loop. The alternative requires flow to surface and a correspondingly higher pressure to drive such a flow path, which can be detrimental to the well. In addition, the progressive cavity pump does not shear the fluid as centrifugal pumps or eductors do. This allows for viscous fluids and gels that are required for certain downhole operations to be pumped downstream without being damaged.
The produced flow will flow upstream into the tubular string 202 via pump opening 118 and through the gapped region 116 at the flow rate of approximately 6 BPM and combine with the driving fluid being urged downstream through the inlet opening 105 at a flow rate of approximately 3 BPM. Consequently, the combined fluid will exit the stator 106 via the outlet opening 107 at a flow rate of approximately 9 BPM and at a pressure of approximately 300 psi. The combined fluid will then flow upstream, for example, to a surface, at the flow rate of 9 BPM because sealing element 204 prevents fluid from flowing downstream. Combining the production flow with the driving fluid can be particularly beneficial when another well's higher pressure, higher temperature, or less viscous product can be used as the driving fluid urged downstream through the inlet opening 105. Doing so may reduce the viscosity of the combined fluids and enhance the production flow of the well in which the tubular string 202 is disposed.
While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims benefit of U.S. Provisional Patent Application Ser. No. 62/399,105, filed on Sep. 23, 2016, which is herein incorporated by reference in its entirety.